feat(web): initial implementation — server, mw, httputil, health (v1.0.0)

Introduces code.nochebuena.dev/einherjar/web — the HTTP transport layer of the
Einherjar framework. Absorbs httpserver, httpmw, and httputil from micro-lib,
replacing gorilla/mux with chi, adopting SecurityBag-native middleware, and
centralizing error handling through a single httputil.Error function.

server:
- Server interface — embeds lifecycle.Component and chi.Router
- Config struct (EINHERJAR_SERVER_* env vars); DefaultConfig
- New(logger, cfg, opts...) Server; WithMiddleware option
- Binds TCP synchronously in OnStart; logs "server: listening" on success
- Graceful shutdown within ShutdownTimeout on OnStop

mw:
- Recover — catches panics, returns 500, logs at Error
- RequestID — injects UUID v7 (UUID v4 fallback) into context and X-Request-ID header
- RequestLogger — structured access log per request
- CORS / CORSAllowAll — chi-based, applied only when origins non-empty
- IPRateLimit / UserRateLimit — pluggable RateLimiterStore interface
- InMemoryRateLimiterStore — token-bucket backed by golang.org/x/time/rate;
  background goroutine evicts stale entries every 5 minutes
- StatusRecorder — wraps ResponseWriter to capture HTTP status code

httputil:
- Handle[Req, Res] / HandleNoBody[Res] / HandleEmpty[Req] — generic handler adapters
- Error(logger, w, r, err) — derives log level from status (≥500→Error, 4xx→Warn,
  499→Info); writes standardized JSON body; logz enriches *xerrors.Err automatically
- JSON(w, status, v) / NoContent(w) — response helpers
- HandlerFunc adapter type

health:
- NewHandler / NewHandlerWithConfig — runs all Checkable checks concurrently;
  returns JSON {status, components} with per-component latency and error
- Config struct (EINHERJAR_HEALTH_CHECK_TIMEOUT, default 5s)

Root factory:
- web.New(logger, cfg...) Server — composes Recover+RequestID+RequestLogger+CORS
  in outermost-first order; CORS applied only when AllowedOrigins non-empty

- server.Server interface and web/server/identifiable.go: embeds observability.Identifiable;
  ModulePath and ModuleVersion read via runtime/debug.ReadBuildInfo() — prints in launcher banner

docs/adr/index.md

@@ -0,0 +1,21 @@
+# ADR Index — web
+
+Module-level architecture decisions for `code.nochebuena.dev/einherjar/web`.
+
+For framework-wide decisions see the
+[Einherjar docs repository](https://code.nochebuena.dev/einherjar/docs).
+
+No module-level ADRs for v1.0.0 — all design decisions were consistent with
+existing framework principles (ADR-001 through ADR-003 from `core`, framework
+ADRs 001–004 from `docs`). No contested choices required a record.
+
+Decisions worth noting (not ADR-worthy individually):
+
+| Decision | Outcome | Rationale |
+|---|---|---|
+| `RateLimiterStore` as interface (not concrete) | Interface only; `InMemoryRateLimiterStore` as default | Allows `cache-valkey` to satisfy it via duck typing without cross-module import |
+| Fail-open rate limiting | Request allowed on store error | Availability preferred over hard enforcement during infrastructure degradation |
+| `last_seen` excluded | Not in v1.0.0 | Application-domain concern; not transport-level middleware |
+| UUID v7 for request IDs | v7 with v4 fallback | Time-ordered IDs sort chronologically in logs; fallback ensures generation never fails |
+| `observability.Checkable` not redefined | Imported from contracts | Starters implement contracts directly; no web import needed by db/cache starters |
+| Background goroutine for in-memory eviction | `time.Ticker` goroutine | Avoids `worker` module dependency; in-memory store is self-contained |