feat(roles): add the read-only pr_reviewer role end-to-end

A global, read-only PR reviewer agent (pr-reviewer-1) that reviews inbound
external/fork PRs and posts one change-request. Wired end-to-end:

- identity: Role.PR_REVIEWER + agent + ROLE_LEVEL (QA-peer) + REVIEWER_ROLES
- lifecycle: CLAIM_RULES + ROLE_TEAM_RULES + a dedicated claim_pr_review /
  post_pr_review verb pair (distinct from QA's) + the pr_review_done action and
  its in_progress->completed transition; give_me_work / i_am_idle gain the role
- role_config: a read-only RoleConfig (allows_write=False)
- journaling: ALL_CELLS read tier so it can read internal intent like QA
- tracing: post_pr_review requires a learning entry; claim_pr_review is waived
- seeds presentation + factory prompt layer + builtin tools + the agentrole
  enum migration (037) + regenerated verb/lifecycle artifacts

Read-only at /app like QA/auditor; default-off — nothing dispatches review work
until external_pr_enabled. Foundation + role-config + enum suites green; ruff +
mypy clean; orchestrator boots.

agents/prompts/_generated/pr_reviewer.md

@@ -0,0 +1,23 @@
+<!-- AUTOGENERATED by scripts/regenerate_verb_tables.py. -->
+<!-- Per-role verb signatures, derived from Pydantic schemas. -->
+
+## Verbs available to you (autogenerated source of truth)
+
+### Flow verbs
+
+| Verb | Body schema |
+|------|-------------|
+| `claim_pr_review` | `claim_pr_review(unknown — no Pydantic schema)` |
+| `give_me_work` | `give_me_work()` |
+| `i_am_idle` | `i_am_idle()` |
+| `post_pr_review` | `post_pr_review(unknown — no Pydantic schema)` |
+
+### Content (do) tools
+
+| Tool | Body schema |
+|------|-------------|
+| `note` | `note(text: str, scope: str = 'note', task_id: UUID | None = None, title: str | None = None, context: str = '', options: list[str | str] | None = None, chosen: str = '', rationale: str = '', consequences: list[str] | None = None, what_done: str = '', what_learned: str = '', what_struggled: str = '', next_steps: list[str] | None = None)` |
+| `evidence` | `evidence(task_id: UUID)` |
+| `notify_list` | `notify_list(unread_only: bool = True, pending_ack_only: bool = False, limit: int = 20)` |
+| `notify_get` | `notify_get(notification_id: UUID)` |
+| `channels` | `channels()` |