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>

docs/plans/2026-08-04-pragent-design.md

@@ -297,3 +297,24 @@ and they may be worth contributing upstream rather than shipping standalone.
 - Auto-fix commits (findings and suggestions only — writing to branches is a later,
   separately-gated decision)
 - Web dashboard (event schema first; dashboard is a downstream consumer)
+
+## Bootstrap: the pilot (2026-08-17)
+
+Before the framework build, a minimal **pilot** was shipped to get a working AI
+review bot live immediately (user decision 2026-08-17). It is deliberately not
+this design:
+
+- Single Python script (`pilot/ai_review.py`, stdlib only) fetched at runtime by
+  a per-repo Gitea Action (`pilot/workflow-template.yml`).
+- One model, `glm-5.2:cloud` via the on-network headroom proxy — no tiering, no
+  analyzer fan-out, no shared-prefix caching, no provider matrix.
+- Trigger = `AI-REVIEW` label on a PR (deterministic skip, the cheapest tier
+  rule, but expressed as a Gitea Actions `if` gate rather than the tier engine).
+- Fail-open, comment-only review; no inline line comments, no status checks,
+  no analytics JSONL, no `explain`/`replay`.
+- Re-posts on every push (no prior-comment synthesis — §6.1 — yet).
+
+The pilot validates the delivery model (CI-step + bot user, not a central
+webhook) and the on-network provider path. When the framework build resumes,
+`pilot/ai_review.py` is replaced by `pragent review`; the per-repo workflow
+stays, just calling the CLI instead of curling the script. See `pilot/README.md`.