feat: initial FastAPI boilerplate setup

Set up Webber - multi-agent AI development system with:

- Domain-based project structure (src/domains/, src/shared/)
- BaseController pattern with lazy router instantiation
- Pydantic Settings configuration with env file support
- Logger decorator with temporal benchmarking and trace IDs
- UserProvider singleton for request-scoped context
- Custom exception hierarchy
- Health endpoints (/, /health)

Dependencies (CVE checked 2026-01-09):
- FastAPI 0.128.0, Starlette 0.50.0, Uvicorn 0.40.0
- Pydantic 2.12.4, PydanticAI 1.40.0
- All packages at latest safe versions

Placeholder domains for future implementation:
- agents/ (explore, plan, task)
- tools/ (file, shell, search)
- auth/ (tatlock integration)

Port: 8086 (per CONTAINERS.md allocation)

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

src/shared/exceptions.py

@@ -0,0 +1,107 @@
+"""
+Custom exception hierarchy.
+
+All application exceptions inherit from AppException.
+"""
+from typing import Any, Optional
+
+
+class AppException(Exception):
+    """Base exception for application errors."""
+
+    def __init__(
+        self,
+        message: str,
+        status_code: int = 500,
+        error_code: Optional[str] = None,
+        details: Optional[dict[str, Any]] = None,
+    ):
+        self.message = message
+        self.status_code = status_code
+        self.error_code = error_code or self.__class__.__name__
+        self.details = details or {}
+        super().__init__(message)
+
+    def to_dict(self) -> dict[str, Any]:
+        """Convert to JSON-serializable dict."""
+        return {
+            "error": self.error_code,
+            "message": self.message,
+            "details": self.details,
+        }
+
+
+class NotFoundError(AppException):
+    """Resource not found."""
+
+    def __init__(self, resource: str, identifier: Any):
+        super().__init__(
+            message=f"{resource} not found: {identifier}",
+            status_code=404,
+            details={"resource": resource, "identifier": str(identifier)},
+        )
+
+
+class ValidationError(AppException):
+    """Input validation failed."""
+
+    def __init__(self, message: str, field: Optional[str] = None):
+        super().__init__(
+            message=message,
+            status_code=422,
+            details={"field": field} if field else {},
+        )
+
+
+class AuthenticationError(AppException):
+    """Authentication required or failed."""
+
+    def __init__(self, message: str = "Authentication required"):
+        super().__init__(message=message, status_code=401)
+
+
+class AuthorizationError(AppException):
+    """Permission denied."""
+
+    def __init__(self, message: str = "Permission denied"):
+        super().__init__(message=message, status_code=403)
+
+
+class ConflictError(AppException):
+    """Resource conflict (e.g., duplicate)."""
+
+    def __init__(self, message: str):
+        super().__init__(message=message, status_code=409)
+
+
+class RateLimitError(AppException):
+    """Rate limit exceeded."""
+
+    def __init__(self, retry_after: int = 60):
+        super().__init__(
+            message="Rate limit exceeded",
+            status_code=429,
+            details={"retry_after": retry_after},
+        )
+
+
+class ServiceUnavailableError(AppException):
+    """External service unavailable."""
+
+    def __init__(self, service: str, message: Optional[str] = None):
+        super().__init__(
+            message=message or f"Service unavailable: {service}",
+            status_code=503,
+            details={"service": service},
+        )
+
+
+class TimeoutError(AppException):
+    """Operation timed out."""
+
+    def __init__(self, operation: str, timeout_seconds: float):
+        super().__init__(
+            message=f"Operation timed out: {operation}",
+            status_code=504,
+            details={"operation": operation, "timeout_seconds": timeout_seconds},
+        )