[bug] .github/hooks/rtk-rewrite.json with broken "rtk hook" command causes spurious parse_failure entries per session

Summary

Users who ran an earlier version of rtk init --copilot (or rtk init when Copilot support was first introduced in #605) end up with a .github/hooks/rtk-rewrite.json containing:

{
  "hooks": {
    "PreToolUse": [
      {
        "type": "command",
        "command": "rtk hook",
        "cwd": ".",
        "timeout": 5
      }
    ]
  }
}

"rtk hook" requires a subcommand (gemini or copilot). Without one, it prints help and exits non-zero. This fires on every Bash tool call, silently logging a parse_failure with raw_command = "hook" in history.db.

Reproduction

1. Have .github/hooks/rtk-rewrite.json with "command": "rtk hook" in your project
2. Run any Bash command through Claude Code
3. Run rtk gain --failures → see Nx hook entries with fallback_succeeded = 0
4. Query the DB directly:

   sqlite3 ~/Library/Application\ Support/rtk/history.db \
     "SELECT error_message FROM parse_failures WHERE raw_command = 'hook' LIMIT 1;"
   

   → Returns the full rtk hook --help output as the error message

Impact

• Inflated failure count in rtk gain --failures
• Spurious fallback_succeeded = 0 entries (no actual fallback occurs — the hook returns non-zero, Claude Code runs the original command unchanged)
• Silent — no visible error to the user

Root cause

Commit #605 (feat(copilot): add Copilot hook support) included .github/hooks/rtk-rewrite.json with "command": "rtk hook" instead of "command": "rtk hook copilot". The fix in the pending Copilot integration (see #823) generates the correct "rtk hook copilot" command, but does not migrate or clean up existing broken files.

Neither rtk init --show nor rtk init --uninstall check .github/hooks/ for orphaned files.

Note: different from #712

Issue #712 reports that rtk init doesn't wire up rtk hook at all. This issue is the inverse: rtk init did write .github/hooks/rtk-rewrite.json, but with an incomplete command that silently breaks on every invocation.

Proposed fix

1. rtk init --show detects .github/hooks/rtk-rewrite.json with "rtk hook" and warns with actionable guidance
2. rtk init -g --uninstall removes the broken file as part of cleanup

PR with the fix is attached.