feat: add dedicated testing agents and enhanced parallel orchestration

Introduce a new testing agent architecture that runs regression tests
independently from coding agents, improving quality assurance in
parallel mode.

Key changes:

Testing Agent System:
- Add testing_prompt.template.md for dedicated testing agent role
- Add feature_mark_failing MCP tool for regression detection
- Add --agent-type flag to select initializer/coding/testing mode
- Remove regression testing from coding prompt (now handled by testing agents)

Parallel Orchestrator Enhancements:
- Add testing agent spawning with configurable ratio (--testing-agent-ratio)
- Add comprehensive debug logging system (DebugLog class)
- Improve database session management to prevent stale reads
- Add engine.dispose() calls to refresh connections after subprocess commits
- Fix f-string linting issues (remove unnecessary f-prefixes)

UI Improvements:
- Add testing agent mascot (Chip) to AgentAvatar
- Enhance AgentCard to display testing agent status
- Add testing agent ratio slider in SettingsModal
- Update WebSocket handling for testing agent updates
- Improve ActivityFeed to show testing agent activity

API & Server Updates:
- Add testing_agent_ratio to settings schema and endpoints
- Update process manager to support testing agent type
- Enhance WebSocket messages for agent_update events

Template Changes:
- Delete coding_prompt_yolo.template.md (consolidated into main prompt)
- Update initializer_prompt.template.md with improved structure
- Streamline coding_prompt.template.md workflow

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

client.py

@@ -59,6 +59,7 @@ FEATURE_MCP_TOOLS = [
     "mcp__features__feature_get_for_regression",
     "mcp__features__feature_mark_in_progress",
     "mcp__features__feature_mark_passing",
+    "mcp__features__feature_mark_failing",  # Mark regression detected
     "mcp__features__feature_skip",
     "mcp__features__feature_create_bulk",
     "mcp__features__feature_create",