Implement status routes

[2witstudios]

Epic 3: REST API Routes — Issue 1/5

Source: Composite — best of each worktree

Description

Read-only status endpoints for manifest data and live agent statuses.

Acceptance Criteria

• GET /api/status — full manifest with live agent statuses (calls checkAgentStatus())
• GET /api/worktrees/:id — single worktree detail with refreshed statuses
• GET /api/worktrees/:id/diff — branch diff (numstat format with file-level additions/deletions)
• All routes authenticated via Bearer token
• Tests: Fastify inject() with mocked core functions

Dependencies

• Requires: Create ppg serve command and Fastify server scaffold #63 (server scaffold), Implement token auth system with hashing and rate limiting #64 (auth), Implement centralized error handler #66 (error handler)

Files to Create/Modify

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