feat: implement Phase 2 two-tier architecture with Steward

Add comprehensive two-tier architecture where Steward analyzes requests
and Tatlock executes with scoped tools. Includes full infrastructure for
request preprocessing, tool tracking, benchmarking, and streaming.

**Added:**
- Steward agent for request analysis and capability recommendation
- Household Registry for centralized capability management
- Request preprocessing pipeline (Steward → Tatlock flow)
- Tool usage tracking and benchmarking system
- Streaming transparency (Steward reasoning visible in streams)
- Structured logging with operation timing
- Redis benchmark storage with 30-day expiry
- Benchmark analysis CLI tools

**Infrastructure:**
- src/agents/steward/ - Steward agent implementation
- src/agents/tatlock_core/ - Tatlock capability domain
- src/core/preprocessing.py - Request preprocessing pipeline
- src/core/tool_tracking.py - Tool call tracking
- src/core/benchmarks.py - Benchmark recording system
- src/core/household_registry.py - Capability registry
- src/core/startup.py - Application startup coordination
- src/core/logging_config.py - Structured logging setup

**Integration:**
- Responses API uses Steward for Tatlock requests
- Chat Completions wraps Responses API for OpenAI compatibility
- Streaming coordinator supports Steward + Tatlock flow
- Tool scoping per request based on Steward recommendations

**Testing:**
- Integration tests for Steward-Tatlock flow
- Benchmark and registry unit tests
- Steward streaming tests

See PHASE2_PLAN.md and PHASE2_COMPLETE.md for detailed documentation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/responses/router.py

@@ -95,13 +95,35 @@ async def create_response(
     logger.info(f"Response request for model: {request.model}")
 
     try:
+        # Check if this is a Tatlock request - use Steward preprocessing (Phase 2)
+        model_id = request.model
+        if "." in model_id:
+            model_id = model_id.split(".", 1)[1]
+
+        use_steward = model_id.lower() == "tatlock"
+
         if request.stream:
             logger.info("Streaming response requested")
-            return EventSourceResponse(
-                service.create_response_stream(request)
-            )
+            if use_steward:
+                logger.info("Streaming with Steward preprocessing for Tatlock request")
+                # Use Steward + Tatlock streaming (Milestone 3.5)
+                from src.responses.streaming import StreamingCoordinator
+                coordinator = StreamingCoordinator()
+                return EventSourceResponse(
+                    coordinator.stream_response_with_steward(request)
+                )
+            else:
+                # Regular streaming for non-Tatlock models
+                return EventSourceResponse(
+                    service.create_response_stream(request)
+                )
 
-        return await service.create_response(request)
+        # Use appropriate service method
+        if use_steward:
+            logger.info("Using Steward preprocessing for Tatlock request")
+            return await service.create_response_with_steward(request)
+        else:
+            return await service.create_response(request)
 
     except ModelNotFoundError as e:
         logger.error(f"Model not found: {e}")