feat(spawn-pr-reviews): add parallel PR review skill using tea/gitea

Creates new user-invocable skill for reviewing PRs:
- Takes multiple PR numbers as arguments
- Creates isolated review worktrees for each PR
- Spawns code-reviewer agents in parallel
- Event-driven result handling
- Posts review comments to Gitea using tea
- Read-only operation (no auto-fixes)

Uses tea and gitea skill (not gh), avoiding conflicts with base
system instructions.

Pattern matches spawn-issues: Haiku orchestrator with allowed-tools
for bash execution.

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

CLAUDE.md

@@ -55,6 +55,7 @@ See the manifesto for our identity, personas, and beliefs about AI-augmented dev
 | `/vision-to-backlog [vision-file]` | Transform product vision into executable backlog via DDD |
 | `/create-milestones` | Organize issues into value-based milestones |
 | `/spawn-issues <n> [<n>...]` | Implement multiple issues in parallel with automated review |
+| `/spawn-pr-reviews <n> [<n>...]` | Review one or more PRs using code-reviewer agents |
 | `/create-capability` | Create new skill, agent, or capability for the architecture |
 | `/capability-writing` | Guide for designing capabilities following best practices |