feature: Add git context to PreToolUse/PostToolUse hook inputs

Summary

PreToolUse/PostToolUse hooks currently lack git context needed for intelligent tool blocking/validation.

Problem

When implementing guardrails in hooks, we need to determine:

• Current branch name
• Whether execution is in a worktree
• Worktree root path
• Whether file is in project root vs worktree

Current workaround: Hooks must call git commands themselves, adding latency and complexity.

Proposed Solution

Add standard fields to PreToolUse/PostToolUse hook input JSON:

{
  "hookInput": {
    "tool_name": "Write",
    "tool_input": {...},
    "git": {
      "branch_name": "release/my-feature",
      "is_worktree": true,
      "worktree_root": "/path/to/.worktrees/my-feature",
      "project_root": "/path/to/repo",
      "is_dirty": false,
      "staged_count": 3
    }
  }
}

Use Cases

1. WorttreeGuard: Block Write/Edit operations on main worktree (check is_worktree flag)
2. MigrationGuard: Warn when creating duplicate migration numbers (check branch_name to filter context-local files)
3. CommitGuard: Detect dangerous commands like git push --force main (branch_name prevents false positives)

Data

• learning_with: 59+ wrong_approach errors from main-worktree edits
• Hook implementations need git context in 70%+ of safety rules

Benefits

• Eliminates subprocess overhead in hooks
• Enables stateless, deterministic validation
• Simpler hook scripts (no shell escaping, git call handling)