refactor: organize pilot packages

Group review, feedback, evaluation, observability, and entrypoint code into packages. Keep thin top-level compatibility shims for existing scripts and imports, and mirror the structure in the tests.

docs/architecture.md

@@ -12,7 +12,7 @@ webhook_server ── trusted base config ──► review_config
           │ bounded worker
           ▼
 review_pr facade/orchestrator
-   ├── gitea_client       fetch diff, reviews, config; publish review
+   ├── entrypoints/gitea  fetch diff, reviews, config; publish review
    ├── diff_compress      reduce prompt context
    ├── opencode_review     isolated checkout + agent execution
    │       └── model / repo factory (.opencode)
@@ -24,20 +24,20 @@ review_pr facade/orchestrator
 ## Seams and responsibilities
 
 The external seam is `ai_review.review_pr(...)`: one call represents one review
-attempt and returns success/skip status. The module is retained as a facade for
-the CI and webhook callers that already import it.
+attempt and returns success/skip status. The top-level module is a compatibility
+shim; the implementation lives in `review/ai_review.py`.
 
 The internal seams are deliberately narrower:
 
 - `review_config.repo_enabled(get, ...)` owns the security-sensitive opt-in
   decision. It receives a transport function, so malformed configuration and
   failure behavior are deterministic in tests.
-- `gitea_client.request()` and `GiteaClient` own HTTP authentication, JSON
+- `entrypoints/gitea.request()` and `GiteaClient` own HTTP authentication, JSON
   request encoding, timeout, and Gitea URL construction.
 - `model_client.complete()` owns the legacy Anthropic-compatible request shape.
   `opencode_review` is the preferred agent adapter and keeps Gitea I/O out of
   the autonomous process.
-- `diff_compress`, finding parsing, config filtering, and rendering remain
+- `review/diff`, finding parsing, config filtering, and rendering remain
   pure transformations. Their callers do not need to know how model or Gitea
   transport works.
 - `langfuse_trace` is an optional sink. It is fail-open and cannot change the