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

pyproject.toml

@@ -4,6 +4,9 @@ version = "v0.3.3"
 description = "AI Agent Compute Network - Main Project"
 authors = ["AITBC Team"]
 
+[tool.poetry.packages]
+aitbc-core = { path = "packages/py/aitbc-core", develop = true }
+
 [tool.poetry.dependencies]
 python = ">=3.13,<3.14"
 # Core Web Framework