feat(spawn-pr-fixers): add parallel PR fixing skill using tea/gitea

Creates new user-invocable skill for fixing PRs based on review feedback:
- Takes multiple PR numbers as arguments
- Creates isolated fix worktrees for each PR
- Spawns pr-fixer agents in parallel
- Event-driven result handling
- Addresses review comments autonomously
- Commits and pushes fixes to Gitea using tea
- Shows detailed summary of all fixes

Uses tea and gitea skill (not gh). Pattern matches spawn-issues and
spawn-pr-reviews: Haiku orchestrator with allowed-tools.

Completes the spawn trilogy:
- spawn-issues: full workflow (implement → review → fix)
- spawn-pr-reviews: review only (read-only)
- spawn-pr-fixers: fix only (based on feedback)

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

CLAUDE.md

@@ -56,6 +56,7 @@ See the manifesto for our identity, personas, and beliefs about AI-augmented dev
 | `/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 |
+| `/spawn-pr-fixers <n> [<n>...]` | Fix one or more PRs based on review feedback |
 | `/create-capability` | Create new skill, agent, or capability for the architecture |
 | `/capability-writing` | Guide for designing capabilities following best practices |