feat(pilot): minimal AI review bot for Gitea Actions

Ships a working pragent pilot ahead of the framework build (design doc
deferred). Single stdlib-only reviewer script fetched at runtime by a per-repo
Gitea Action; reviews fire only on PRs with the AI-REVIEW label; model is
glm-5.2:cloud via the on-network headroom proxy; fail-open.

- pilot/ai_review.py: fetch PR diff, call model, post review as pragent-bot
- pilot/workflow-template.yml: per-repo Gitea Action gated on AI-REVIEW label
- pilot/README.md: onboarding (bot collaborator + secret + workflow + label)
- tests/pilot/test_ai_review.py: 15 unit tests for pure helpers (no network)
- README/design doc: note pilot is the bootstrap; framework build deferred

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -3,8 +3,12 @@
 An extensible, forge-agnostic PR review framework. Not a product — a toolkit that teams
 extend with their own review dimensions.
 
-**Status:** design approved, implementation not started. See
-[`docs/plans/2026-08-04-pragent-design.md`](docs/plans/2026-08-04-pragent-design.md).
+**Status:** design approved; framework build deferred. A **pilot** is live — a
+minimal AI review bot running as a Gitea Actions step on `glm-5.2:cloud`. See
+[`pilot/README.md`](pilot/README.md) to onboard a repo. The framework design
+remains at [`docs/plans/2026-08-04-pragent-design.md`](docs/plans/2026-08-04-pragent-design.md);
+the pilot is its bootstrap and will be superseded by `pragent review` when the
+framework build resumes.
 
 ## What it is