Initial commit: RSS platform phase 1 skeleton with code review fixes

Features:
- FastAPI + SQLAlchemy 2.0 async + PostgreSQL/pgvector + Redis backend
- Vue 3 + TypeScript + Element Plus frontend
- JWT auth with access/refresh tokens and revocation
- Admin/member RBAC
- RSS feed CRUD and article listing
- Settings management with Fernet encryption for sensitive values
- Redis distributed lock service
- Alembic initial migration
- Docker Compose development environment

Fixes from code review:
- Fix DB session leak in dependency injection
- Restrict registration to admin only
- Add default admin password warning
- Implement JWT refresh tokens and jti blacklist
- Strengthen password policy
- Use func.count for pagination totals
- Replace NullPool with AsyncAdaptedQueuePool
- Remove init_db from lifespan to enforce alembic migrations
- Add request_id middleware and logging filter
- Fix vite.config.ts env loading
- Add frontend token refresh interceptor
- Add Vue error handler

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/core/exceptions.py

@@ -0,0 +1,64 @@
+"""Custom exceptions and error handlers."""
+from fastapi import FastAPI, Request
+from fastapi.responses import JSONResponse
+
+from app.core.logging import get_logger
+
+logger = get_logger(__name__)
+
+
+class PlatformException(Exception):
+    """Base exception for the platform."""
+
+    def __init__(self, message: str, status_code: int = 400):
+        super().__init__(message)
+        self.message = message
+        self.status_code = status_code
+
+
+class AuthenticationError(PlatformException):
+    """Authentication failed."""
+
+    def __init__(self, message: str = "Authentication failed"):
+        super().__init__(message, status_code=401)
+
+
+class AuthorizationError(PlatformException):
+    """Authorization failed."""
+
+    def __init__(self, message: str = "Forbidden"):
+        super().__init__(message, status_code=403)
+
+
+class NotFoundError(PlatformException):
+    """Resource not found."""
+
+    def __init__(self, message: str = "Resource not found"):
+        super().__init__(message, status_code=404)
+
+
+class ConflictError(PlatformException):
+    """Resource conflict."""
+
+    def __init__(self, message: str = "Conflict"):
+        super().__init__(message, status_code=409)
+
+
+def add_exception_handlers(app: FastAPI) -> None:
+    """Register global exception handlers."""
+
+    @app.exception_handler(PlatformException)
+    async def platform_exception_handler(request: Request, exc: PlatformException):
+        logger.warning("Platform exception: %s", exc.message)
+        return JSONResponse(
+            status_code=exc.status_code,
+            content={"detail": exc.message},
+        )
+
+    @app.exception_handler(Exception)
+    async def generic_exception_handler(request: Request, exc: Exception):
+        logger.exception("Unhandled exception: %s", exc)
+        return JSONResponse(
+            status_code=500,
+            content={"detail": "Internal server error"},
+        )