feat(tier4): Add patch generation for auto-patching

- Add TIER4_PATCH_PROMPT to mma_prompts.py with unified diff format
- Add run_tier4_patch_generation function to ai_client.py
- Import mma_prompts in ai_client.py
- Add unit tests for patch generation

conductor/tracks/tier4_auto_patching_20260306/plan.md

@@ -5,8 +5,8 @@
 ## Phase 1: Patch Generation
 Focus: Generate unified diff on test failure
 
-- [ ] Task 1.1: Initialize MMA Environment
-- [ ] Task 1.2: Extend Tier 4 prompt for patch generation
+- [x] Task 1.1: Initialize MMA Environment
+- [~] Task 1.2: Extend Tier 4 prompt for patch generation
     - WHERE: `src/mma_prompts.py` or inline in `ai_client.py`
     - WHAT: Prompt to generate unified diff
     - HOW: