Extract shared utilities to aitbc-core package

- Updated aitbc-core pyproject.toml with structlog and starlette dependencies
- Created middleware directory with 4 middleware files:
  - RequestIDMiddleware for request correlation
  - PerformanceLoggingMiddleware for performance tracking
  - RequestValidationMiddleware for size validation
  - ErrorHandlerMiddleware for standardized error responses
- Added structlog logging functions (configure_logging, get_logger) to aitbc-core
- Updated coordinator-api main.py to use aitbc-core middleware and logging
- Removed local middleware files from coordinator-api
- Removed app_logging.py from coordinator-api
- Added aitbc-core as workspace package to root pyproject.toml

This completes Phase 4.1: Extract shared utilities to aitbc-core

apps/coordinator-api/src/app/main.py

@@ -91,11 +91,13 @@ except ImportError:
     print("WARNING: ML ZK proofs router not available (missing dependencies)")
 from aitbc import get_logger
 
-from .app_logging import configure_logging
-from .middleware.request_id import RequestIDMiddleware
-from .middleware.performance import PerformanceLoggingMiddleware
-from .middleware.validation import RequestValidationMiddleware
-from .middleware.error_handler import ErrorHandlerMiddleware
+from aitbc.logging import configure_logging
+from aitbc import (
+    RequestIDMiddleware,
+    PerformanceLoggingMiddleware,
+    RequestValidationMiddleware,
+    ErrorHandlerMiddleware,
+)
 from .exceptions import AITBCError, ErrorResponse
 
 # Configure structured logging