feat: update project structure and docs

app/common/__init__.py

@@ -0,0 +1 @@
+"""Common utilities and shared components."""

app/common/error_handler.py

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+"""Common error response schema and exception handlers."""
+
+from datetime import datetime
+
+from fastapi import FastAPI, Request
+from fastapi.responses import JSONResponse
+from pydantic import BaseModel
+from starlette.exceptions import HTTPException
+
+from app.core.exceptions import AppException
+
+
+class ErrorResponse(BaseModel):
+    """Standard error response format."""
+
+    status_code: int
+    message: str
+    details: dict | None = None
+    timestamp: str
+
+
+async def app_exception_handler(request: Request, exc: AppException) -> JSONResponse:
+    """Handle application exceptions with standard response."""
+    return JSONResponse(
+        status_code=exc.status_code,
+        content={
+            "status_code": exc.status_code,
+            "message": exc.message,
+            "timestamp": datetime.utcnow().isoformat(),
+        },
+    )
+
+
+async def http_exception_handler(request: Request, exc: HTTPException) -> JSONResponse:
+    """Handle HTTP exceptions with standard response."""
+    return JSONResponse(
+        status_code=exc.status_code,
+        content={
+            "status_code": exc.status_code,
+            "message": str(exc.detail),
+            "timestamp": datetime.utcnow().isoformat(),
+        },
+    )
+
+
+def register_exception_handlers(app: FastAPI):
+    """Register all exception handlers with FastAPI app."""
+    app.add_exception_handler(
+        AppException,
+        app_exception_handler,  # type: ignore[arg-type]
+    )
+    app.add_exception_handler(
+        HTTPException,
+        http_exception_handler,  # type: ignore[arg-type]
+    )