[codex] fix: disable Gemini PreToolUse hook install

[heyramzi]

Summary

• stop installing the Gemini PreToolUse managed hook from Orca
• sweep stale managed Gemini hook entries from removed event buckets during reinstall
• add a regression test that proves reinstall removes an existing PreToolUse hook from ~/.gemini/settings.json

Root Cause

Orca was auto-installing a managed Gemini PreToolUse hook into ~/.gemini/settings.json. In some Gemini CLI environments that hook payload is rejected during tool dispatch, which turns a dashboard status integration into a tool-execution blocker. Reinstall also left stale PreToolUse entries behind because the Gemini installer only updated currently subscribed events and never cleaned removed ones.

Impact

• Gemini sessions keep the dashboard-safe lifecycle hooks (BeforeAgent, AfterAgent, AfterTool)
• Orca no longer injects the problematic PreToolUse hook for Gemini
• existing stale managed PreToolUse entries are removed on reinstall instead of persisting forever

Validation

• pnpm test src/main/gemini/hook-service.test.ts
• pnpm typecheck:node