Add ruff linter/formatter for Python

- Add ruff as dev dependency
- Configure ruff in pyproject.toml with strict 88-char line limit
- Ignore B008 (FastAPI Depends pattern is standard)
- Allow longer lines in tests for readability
- Fix all lint issues in source files
- Add Makefile targets: lint-backend, format-backend, fix-backend

backend/routes/invites.py

@@ -1,25 +1,29 @@
 """Invite routes for public check, user invites, and admin management."""
-from datetime import datetime, timezone
 
-from fastapi import APIRouter, Depends, HTTPException, status, Query
-from sqlalchemy import select, func, desc
+from datetime import UTC, datetime
+
+from fastapi import APIRouter, Depends, HTTPException, Query, status
+from sqlalchemy import desc, func, select
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from auth import require_permission
 from database import get_db
-from invite_utils import generate_invite_identifier, normalize_identifier, is_valid_identifier_format
-from models import User, Invite, InviteStatus, Permission
+from invite_utils import (
+    generate_invite_identifier,
+    is_valid_identifier_format,
+    normalize_identifier,
+)
+from models import Invite, InviteStatus, Permission, User
 from schemas import (
+    AdminUserResponse,
     InviteCheckResponse,
     InviteCreate,
     InviteResponse,
-    UserInviteResponse,
     PaginatedInviteRecords,
-    AdminUserResponse,
+    UserInviteResponse,
 )
 
-
 router = APIRouter(prefix="/api/invites", tags=["invites"])
 admin_router = APIRouter(prefix="/api/admin", tags=["admin"])
 
@@ -54,9 +58,7 @@ async def check_invite(
     if not is_valid_identifier_format(normalized):
         return InviteCheckResponse(valid=False, error="Invalid invite code format")
 
-    result = await db.execute(
-        select(Invite).where(Invite.identifier == normalized)
-    )
+    result = await db.execute(select(Invite).where(Invite.identifier == normalized))
     invite = result.scalar_one_or_none()
 
     # Return same error for not found, spent, and revoked to avoid information leakage
@@ -112,9 +114,7 @@ async def create_invite(
 ) -> InviteResponse:
     """Create a new invite for a specified godfather user."""
     # Validate godfather exists
-    result = await db.execute(
-        select(User.id).where(User.id == data.godfather_id)
-    )
+    result = await db.execute(select(User.id).where(User.id == data.godfather_id))
     godfather_id = result.scalar_one_or_none()
     if not godfather_id:
         raise HTTPException(
@@ -141,8 +141,8 @@ async def create_invite(
             if attempt == MAX_INVITE_COLLISION_RETRIES - 1:
                 raise HTTPException(
                     status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
-                    detail="Failed to generate unique invite code. Please try again.",
-                )
+                    detail="Failed to generate unique invite code. Try again.",
+                ) from None
 
     if invite is None:
         raise HTTPException(
@@ -156,7 +156,9 @@ async def create_invite(
 async def list_all_invites(
     page: int = Query(1, ge=1),
     per_page: int = Query(10, ge=1, le=100),
-    status_filter: str | None = Query(None, alias="status", description="Filter by status: ready, spent, revoked"),
+    status_filter: str | None = Query(
+        None, alias="status", description="Filter by status: ready, spent, revoked"
+    ),
     godfather_id: int | None = Query(None, description="Filter by godfather user ID"),
     db: AsyncSession = Depends(get_db),
     _current_user: User = Depends(require_permission(Permission.MANAGE_INVITES)),
@@ -175,8 +177,9 @@ async def list_all_invites(
         except ValueError:
             raise HTTPException(
                 status_code=400,
-                detail=f"Invalid status: {status_filter}. Must be ready, spent, or revoked",
-            )
+                detail=f"Invalid status: {status_filter}. "
+                "Must be ready, spent, or revoked",
+            ) from None
 
     if godfather_id:
         query = query.where(Invite.godfather_id == godfather_id)
@@ -224,11 +227,12 @@ async def revoke_invite(
     if invite.status != InviteStatus.READY:
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
-            detail=f"Cannot revoke invite with status '{invite.status.value}'. Only READY invites can be revoked.",
+            detail=f"Cannot revoke invite with status '{invite.status.value}'. "
+            "Only READY invites can be revoked.",
         )
 
     invite.status = InviteStatus.REVOKED
-    invite.revoked_at = datetime.now(timezone.utc)
+    invite.revoked_at = datetime.now(UTC)
     await db.commit()
     await db.refresh(invite)