Implement worktree routes

[2witstudios]

Epic 3: REST API Routes — Issue 4/5

Source: 1-agent worktree — most complete with PR creation

Description

Worktree action endpoints for merge, kill, and PR creation.

Acceptance Criteria

• POST /api/worktrees/:id/merge — calls core/operations/merge (squash/no-ff, force flag, cleanup)
• POST /api/worktrees/:id/kill — kill all agents in worktree
• POST /api/worktrees/:id/pr — create GitHub PR via gh CLI, store URL in manifest
• Merge strategy configurable (squash default, no-ff option)
• Tests with mocked core functions

Dependencies

• Requires: Extract merge operation to core/operations/merge.ts #59 (merge operation), Extract kill operation to core/operations/kill.ts #61 (kill operation), Create ppg serve command and Fastify server scaffold #63 (server scaffold), Implement token auth system with hashing and rate limiting #64 (auth)

Files to Create/Modify

• src/server/routes/worktrees.ts (new)
• src/server/routes/worktrees.test.ts (new)