docs: adopt Conventional Commits and land planning docs

- CONVENTIONAL-COMMITS.md: vendored spec (v1.0.0); CLAUDE.md requires
  agent-written commits to follow it
- tasks 0002-0020: remaining task breakdown of the gitea-axi spec
  (0019 reframed around the three-tier test taxonomy: unit,
  integration, end-to-end)
- spec, CONTEXT.md, and ADRs 0006/0007/0011: pending design
  refinements from the planning sessions

.claude/tasks/0013-pr-review.md

@@ -0,0 +1,19 @@
+---
+spec: gitea-axi
+blocked-by: 0001-scaffold-and-issue-list-core
+---
+
+## What to build
+
+`pr review <n>` with the three action flags `--approve`, `--request-changes`, `--comment`, plus `--body`/`--body-file`.
+Exactly one action flag is required: zero or multiple yield `VALIDATION_ERROR` before any API call, mirroring the merge shorthand-conflict rule.
+Body requirements are not pre-validated locally — if Gitea rejects a body-less review event, its 422 surfaces as `VALIDATION_ERROR` with the server's message.
+Output: `review: { number, action }`.
+
+## Acceptance criteria
+
+- [ ] Each action flag submits the corresponding review event and outputs `review: { number, action }`
+- [ ] Zero action flags, or more than one, yield `VALIDATION_ERROR` (exit 2) with no API call
+- [ ] A server-side 422 for a missing body surfaces as `VALIDATION_ERROR` carrying Gitea's message
+- [ ] `--body-file` works as everywhere else
+- [ ] Fixture-server tests cover all three actions, the flag-count validations, and the 422 passthrough