feat: add qa_build mode, tests, and region mode support

Router Configuration:
- Add mode='qa_build' routing rule in router-config.yml
- Priority 8, uses local_qwen3_8b for Q&A generation

2-Stage Q&A Pipeline Tests:
- Create test_qa_pipeline.py with comprehensive tests
- Test prompt building, JSON parsing, router integration
- Mock DAGI Router responses for testing

Region Mode (Grounding OCR):
- Add region_bbox and region_page parameters to ParseRequest
- Support region mode in local_runtime with bbox in prompt
- Update endpoints to accept region parameters (x, y, width, height, page)
- Validate region parameters and filter pages for region mode
- Pass region_bbox through inference pipeline

Updates:
- Update local_runtime to support region_bbox in prompts
- Update inference.py to pass region_bbox to local_runtime
- Update endpoints.py to handle region mode parameters

router-config.yml

@@ -95,6 +95,14 @@ routing:
     use_llm: local_qwen3_8b
     description: "microDAO chat → local LLM with RBAC context"
 
+  # Q&A Builder mode (for parser-service 2-stage pipeline)
+  - id: qa_build_mode
+    priority: 8
+    when:
+      mode: qa_build
+    use_llm: local_qwen3_8b
+    description: "Q&A generation from parsed documents → local LLM"
+
   # NEW: CrewAI workflow orchestration
   - id: crew_mode
     priority: 3