Server: cleanup tmpclaude dirs when stopped

[gabelul]

Adds a safe cleaner for Claude Code CLI scratch dirs (tmpclaude-*) in project roots.

• Runs only when the agent is not running (after lock check, and after stop).
• Best-effort: ignores failures (Windows locks).
• Env knobs:
  • AUTOCODER_CLEAN_TMPCLAUDE=0 disables
  • AUTOCODER_TMPCLAUDE_MAX_AGE_S= only delete older dirs

Tests:

• pytest -q