feat: add recovery middleware to handle panic gracefully

[hhc7]

Fixes #1536

Proposed Changes

• Add middleware.Recovery() that catches panics from any subsequent middleware or handler, logs the panic message with full stack trace via log.Errorf + debug.Stack(), and returns a unified 500 JSON response (reason: base.unknown) via handler.NewRespBody + TrMsg — consistent with how other errors are handled in internal/base/handler/handler.go.
• Mount Recovery() as the first middleware in internal/base/server/http.go so it covers all subsequent middleware (brotli, accept-language, short-id, auth, etc.) and handlers.
• Add unit tests in recovery_test.go covering both the panic path (verifies 500 + base.unknown reason) and the no-panic path (verifies normal requests pass through unaffected).