refactor(server)!: remove Server.Audit, use Router.Use() middleware

[benitogf]

Summary

Closes #146 — Server.Audit and its companions are gone; consumers gate
requests by registering middleware on server.Router.Use(...).

• The bool-returning Server.Audit hook, AuditHandler, and the
  explorer's AuditFunc are removed from the public API.
• Built-in REST handlers, WebSocket upgrades, custom endpoints, proxy
  routes, and the explorer UI all dispatch through the standard
  gorilla/mux middleware chain — one extension point, no parallel
  mechanisms.
• The JWT auth sample and the static-routes/filters sample demonstrate
  the middleware-based pattern.
• An internal doc comment that claimed Router.Use() middlewares were
  silently dropped on dispatch is corrected — gorilla/mux's Match
  builds the chain into the matched handler before returning, so
  middleware already fans out today. The PR removes the redundant
  parallel mechanism rather than adding new machinery.

Known non-blockers folded into the PR

• The sample directory name samples/static_routes_filters_audit/ is
  intentionally left in place — the heading and code inside have been
  updated, but renaming the directory would break any external links.
  Future cosmetic rename is fair game.
• The exported ErrNotAuthorized sentinel is kept for consumers who
  want to return it from their own middleware. Drop it later if no
  external consumer adopts it.

Test plan

• go test ./... passes (verified locally, race + non-race).
• go vet ./... clean.
• No production code path still references Server.Audit,
  AuditHandler, or AuditFunc.
• The JWT sample boots and rejects unauthenticated requests to
  /data/* while allowing /register and /authorize.
• The static-routes sample rejects requests without the
  X-API-Key: secret header on every dispatched path (REST,
  explorer UI, custom endpoints).
• WebSocket subscriptions are gated by the middleware chain — a
  deny-all middleware refuses the upgrade cleanly with 401, no
  half-upgraded connections.

---

🤖 Generated with Claude Code

[CBosch101]

Clean breaking refactor: Server.Audit / AuditHandler / ui.Handler.AuditFunc are gone, request gating moves to Router.Use() middleware. The central correctness claim holds — verified, not assumed.

Verified

• The "middleware fans out" claim is real for this dispatch path: gorilla/mux (v1.8.1) Router.Match builds the middleware chain into match.Handler when MatchErr == nil, and syncRouter.ServeHTTP (ooo.go:65-88) dispatches match.Handler — so REST, WebSocket upgrades, custom Endpoints, proxy routes, and the explorer UI are all gated by one chain. The corrected doc comment (ooo.go:46-52, replacing the old "not fanned out" claim) matches actual behavior.
• 404/405 correctly skip the chain: Match only wraps when MatchErr == nil, and syncRouter.ServeHTTP handles method-mismatch/not-found before invoking any handler (ooo.go:79-86) — consistent with the README and the doc comment.
• The clock WS path is safe after dropping its inline check (clock.go): clock is reached only via ClockFunc inside the explorer handler (ui/ui.go:159-160), which is route-registered at / and therefore middleware-wrapped.
• No lingering references to the removed API in non-test code; the renamed/rewritten gating tests pass, and go build/go vet/go test -race are clean on the affected packages. The LimitBody short-circuit note (rest.go) is updated correctly to state deny middleware must not call next.

No blockers. The breaking removal is intentional and the migration is mechanical (set a Router.Use(...) middleware instead of Server.Audit), shown in both samples and the README.

---

🤖 Generated with Claude Code