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

server/server_impl.go

@@ -0,0 +1,103 @@
+package server
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+
+	"code.nochebuena.dev/einherjar/contracts/logging"
+	"code.nochebuena.dev/einherjar/contracts/observability"
+	"code.nochebuena.dev/einherjar/core/xerrors"
+)
+
+var _ Server = (*impl)(nil)
+var _ observability.Identifiable = (*impl)(nil)
+
+type impl struct {
+	chi.Router
+	logger logging.Logger
+	cfg    Config
+	opts   serverOpts
+	srv    *http.Server
+}
+
+// New creates a [Server]. No middleware is applied by default; use [WithMiddleware]
+// to compose the middleware stack before passing it to [launcher.New].
+func New(logger logging.Logger, cfg Config, opts ...Option) Server {
+	o := serverOpts{}
+	for _, opt := range opts {
+		opt(&o)
+	}
+	return &impl{
+		Router: chi.NewRouter(),
+		logger: logger,
+		cfg:    cfg,
+		opts:   o,
+	}
+}
+
+// OnInit applies registered middleware to the router.
+func (s *impl) OnInit() error {
+	for _, mw := range s.opts.middleware {
+		s.Router.Use(mw)
+	}
+	return nil
+}
+
+// OnStart binds the TCP listener synchronously so that a port conflict surfaces
+// immediately — the launcher can trigger a clean shutdown instead of running
+// silently without an HTTP server. Requests are served in a background goroutine.
+func (s *impl) OnStart() error {
+	host := s.cfg.Host
+	if host == "" {
+		host = "0.0.0.0"
+	}
+	port := s.cfg.Port
+	if port == 0 {
+		port = 8080
+	}
+	addr := fmt.Sprintf("%s:%d", host, port)
+
+	ln, err := net.Listen("tcp", addr)
+	if err != nil {
+		return xerrors.Unavailable("server: bind %s", addr).WithError(err)
+	}
+
+	s.srv = &http.Server{
+		Addr:         addr,
+		Handler:      s.Router,
+		ReadTimeout:  s.cfg.ReadTimeout,
+		WriteTimeout: s.cfg.WriteTimeout,
+		IdleTimeout:  s.cfg.IdleTimeout,
+	}
+	go func() {
+		if err := s.srv.Serve(ln); err != nil && !errors.Is(err, http.ErrServerClosed) {
+			s.logger.Error("server: fatal", err)
+		}
+	}()
+	s.logger.Info("server: listening", "addr", addr)
+	return nil
+}
+
+// OnStop performs a graceful shutdown, waiting up to ShutdownTimeout for
+// in-flight requests to complete. No-op if OnStart was never called.
+func (s *impl) OnStop() error {
+	if s.srv == nil {
+		return nil
+	}
+	s.logger.Info("server: shutting down")
+	timeout := s.cfg.ShutdownTimeout
+	if timeout == 0 {
+		timeout = defaultShutdownTimeout
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+	if err := s.srv.Shutdown(ctx); err != nil {
+		return xerrors.Internal("server: shutdown").WithError(err)
+	}
+	return nil
+}