feat(mcp): initial implementation — MCP server, framework indexer, 10 tools, 8 validation rules (v0.1.0)

Introduces code.nochebuena.dev/einherjar/mcp — the Einherjar Model Context Protocol
server. A remote, streamable-HTTP service that teaches AI assistants about every
other module of the framework: which package exposes which type, what each module
guarantees through its compliance tests, the canonical wiring shape for a service,
and whether a Go snippet follows the conventions. Indexes the framework on disk at
build time and ships a self-contained binary via go:embed; imports nothing from
other einherjar/* modules at compile time.

server (cmd/server):
- Streamable-HTTP MCP server built on github.com/modelcontextprotocol/go-sdk v1.0.0
- mcp.NewServer + mcp.NewStreamableHTTPHandler, served via net/http on EINHERJAR_MCP_ADDR
  (default :8080) and EINHERJAR_MCP_PATH (default /mcp)
- /healthz liveness endpoint; structured JSON logging via log/slog
- Loads the embedded data/index.json once at startup; in-memory for the process lifetime

indexer (cmd/indexer):
- Walks an Einherjar repository checkout (default ../), parses every sibling
  module's go.mod, README.md, CHANGELOG.md, docs/adr/ADR-*.md, doc.go package
  comments, every exported type/interface/func/method/const/var (via go/doc on
  go/parser ASTs), and compliance_test.go
- Captures module dependency edges by regex over each go.mod's require lines
  (einherjar/* paths only; self-reference filtered)
- Appends a synthetic "wire" module documenting canonical application wiring
  conventions, authored at internal/index/builtins/README.md and embedded via
  go:embed; participates in list_modules / get_module / get_example like a real module

internal/index:
- Schema einherjar.mcp/index/v1; types: Index, Module, SubPackage, Symbol, ADR,
  Example, Compliance, InterfaceAssert, ComplianceTest
- Build(repoRoot) → *Index walks the repo; BuildBuiltins() returns the synthetic
  wire module from the embedded markdown
- Load([]byte) → *Index validates the schema version on read
- FindModule, SearchSymbols helpers used by tools

internal/tools (10 tools):
- list_modules — enumerate every module with purpose + sub-packages
- get_module — package doc, dependencies, sub-packages, key symbols, ADRs,
  compliance counts; optional embedded README
- search_symbols — full-text across name, doc, sub-package, module; filterable by
  module and kind
- get_symbol — full signature, doc comment, source file:line for one symbol
- list_adrs — list ADRs across the framework or within one module
- get_adr — fetch one ADR's markdown body
- get_example — canonical usage snippets extracted from module READMEs and from
  the synthetic wire conventions
- get_compliance — interface assertions (var _ Iface = impl) and structural test
  names from a module's compliance_test.go
- get_changelog — full CHANGELOG.md markdown for one module
- validate_snippet — pattern-match a Go snippet against framework conventions

internal/rules (8 rules, registered via init() against a single registered slice):
- launcher.missing-run — launcher constructed but Run() never called
- launcher.no-components — launcher.New() called without any .Append(...)
- launcher.run-error-discarded — lc.Run() invoked as an ExprStmt (return ignored)
- logz.direct-env-read — os.Getenv("EINHERJAR_LOG_*") bypassing logz config
- web.server-not-appended — web/server constructed but not added to the launcher
- wire.hook-bad-signature — with<Feature>(...) first param is not launcher.Launcher
- wire.hook-outside-beforestart — repo/service/handler construction or route
  registration at the top level of a hook (outside lc.BeforeStart)
- wire.route-specific-after-param — /users/{id} registered before a sibling
  /users/me of the same length and method (chi would shadow the literal route)

Synthetic wire module (internal/index/builtins/README.md):
- Project layout (cmd/<app>/main.go + internal/wire/*.go + per-feature domain dirs)
- Canonical Run() shape: config → logger → infra (db, cache, pool, mc, srv) → cross-
  cutting (validator, permission provider) → launcher.New → lc.Append(infra...) →
  withMigrations / withSuperAdminSeed / withHealth / withFeature hooks → return lc.Run()
- Canonical with<Feature> hook shape: signature (launcher.Launcher first, server.Server
  second, deps last), single lc.BeforeStart closure containing all construction +
  route registration
- chi route ordering, srv.With(authz(...)) authorization, middleware helpers
  (authz / skipPublicPaths / skipMethodPath), tokenSignerAdapter pattern showing
  that the framework exposes Signer.Sign as a primitive and the application owns
  the access/refresh response shape

Packaging:
- Multi-stage Dockerfile that builds from the einherjar repository root
  (docker build -f mcp/Dockerfile .) so cmd/indexer can walk every sibling module
  at image-build time; runtime layer is gcr.io/distroless/static-debian12:nonroot
- 86-byte placeholder data/index.json committed once with `git add -f`; subsequent
  indexer runs overwrite it locally but the file is .gitignored
- .gitea/CODEOWNERS and pull_request_template.md mirror the sibling layout

Design notes:
- mcp depends on nothing in einherjar/* — it reads the framework via the filesystem
  at index time. This keeps mcp outside the framework dependency graph and lets it
  index any version of einherjar without versioning itself in lock-step.
- All structured-output tool responses initialise empty slices ([]Type{}) rather
  than relying on Go's nil-marshals-to-null default, so the SDK's JSON-schema
  output validator never rejects a tools/call result.

internal/tools/get_module.go

@@ -0,0 +1,103 @@
+package tools
+
+import (
+	"context"
+
+	"code.nochebuena.dev/einherjar/mcp/internal/index"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+type getModuleInput struct {
+	Name          string `json:"name" jsonschema:"the module name, e.g. core, web, auth-jwt"`
+	IncludeReadme bool   `json:"includeReadme,omitempty" jsonschema:"when true, embed the full README markdown in the response"`
+}
+
+type getModuleOutput struct {
+	Name        string             `json:"name"`
+	ImportPath  string             `json:"importPath"`
+	Purpose     string             `json:"purpose"`
+	Doc         string             `json:"doc"`
+	GoVersion   string             `json:"goVersion"`
+	DependsOn   []string           `json:"dependsOn"`
+	SubPackages []index.SubPackage `json:"subPackages"`
+	KeySymbols  []symbolHeader     `json:"keySymbols"`
+	ADRs        []adrHeader        `json:"adrs"`
+	Compliance  complianceSummary  `json:"compliance"`
+	Readme      string             `json:"readme,omitempty"`
+}
+
+type complianceSummary struct {
+	InterfaceAssertCount int `json:"interfaceAssertCount"`
+	TestCount            int `json:"testCount"`
+}
+
+type symbolHeader struct {
+	Kind       string `json:"kind"`
+	Name       string `json:"name"`
+	SubPackage string `json:"subPackage"`
+	Signature  string `json:"signature"`
+}
+
+type adrHeader struct {
+	ID    string `json:"id"`
+	Title string `json:"title"`
+}
+
+func registerGetModule(s *mcp.Server, idx *index.Index) {
+	mcp.AddTool(s, &mcp.Tool{
+		Name:        "get_module",
+		Description: "Describe one Einherjar module: sub-packages, key exported symbols (types/interfaces/funcs), and ADRs. Set includeReadme=true to also receive the README markdown.",
+	}, func(ctx context.Context, req *mcp.CallToolRequest, args getModuleInput) (*mcp.CallToolResult, getModuleOutput, error) {
+		m := idx.FindModule(args.Name)
+		if m == nil {
+			return errorResult("module not found: " + args.Name), getModuleOutput{}, nil
+		}
+
+		key := make([]symbolHeader, 0, len(m.Symbols))
+		for _, sym := range m.Symbols {
+			if sym.Kind == "type" || sym.Kind == "interface" || sym.Kind == "func" {
+				key = append(key, symbolHeader{
+					Kind: sym.Kind, Name: sym.Name, SubPackage: sym.SubPackage, Signature: sym.Signature,
+				})
+			}
+		}
+
+		adrs := make([]adrHeader, 0, len(m.ADRs))
+		for _, a := range m.ADRs {
+			adrs = append(adrs, adrHeader{ID: a.ID, Title: a.Title})
+		}
+
+		subs := make([]index.SubPackage, 0, len(m.SubPackages))
+		for _, sp := range m.SubPackages {
+			if sp.Name == "" {
+				continue
+			}
+			subs = append(subs, sp)
+		}
+
+		deps := m.DependsOn
+		if deps == nil {
+			deps = []string{}
+		}
+
+		out := getModuleOutput{
+			Name:        m.Name,
+			ImportPath:  m.ImportPath,
+			Purpose:     m.Purpose,
+			Doc:         m.Doc,
+			GoVersion:   m.GoVersion,
+			DependsOn:   deps,
+			SubPackages: subs,
+			KeySymbols:  key,
+			ADRs:        adrs,
+			Compliance: complianceSummary{
+				InterfaceAssertCount: len(m.Compliance.InterfaceAsserts),
+				TestCount:            len(m.Compliance.Tests),
+			},
+		}
+		if args.IncludeReadme {
+			out.Readme = m.Readme
+		}
+		return jsonText(out), out, nil
+	})
+}