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/schemas.py

@@ -1,5 +1,6 @@
 """Pydantic schemas for API request/response models."""
-from datetime import datetime, date, time
+
+from datetime import date, datetime, time
 from typing import Generic, TypeVar
 
 from pydantic import BaseModel, EmailStr, field_validator
@@ -9,6 +10,7 @@ from shared_constants import NOTE_MAX_LENGTH
 
 class UserCredentials(BaseModel):
     """Base model for user email/password."""
+
     email: EmailStr
     password: str
 
@@ -19,6 +21,7 @@ UserLogin = UserCredentials
 
 class UserResponse(BaseModel):
     """Response model for authenticated user info."""
+
     id: int
     email: str
     roles: list[str]
@@ -27,6 +30,7 @@ class UserResponse(BaseModel):
 
 class RegisterWithInvite(BaseModel):
     """Request model for registration with invite."""
+
     email: EmailStr
     password: str
     invite_identifier: str
@@ -34,12 +38,14 @@ class RegisterWithInvite(BaseModel):
 
 class SumRequest(BaseModel):
     """Request model for sum calculation."""
+
     a: float
     b: float
 
 
 class SumResponse(BaseModel):
     """Response model for sum calculation."""
+
     a: float
     b: float
     result: float
@@ -47,6 +53,7 @@ class SumResponse(BaseModel):
 
 class CounterRecordResponse(BaseModel):
     """Response model for a counter audit record."""
+
     id: int
     user_email: str
     value_before: int
@@ -56,6 +63,7 @@ class CounterRecordResponse(BaseModel):
 
 class SumRecordResponse(BaseModel):
     """Response model for a sum audit record."""
+
     id: int
     user_email: str
     a: float
@@ -69,6 +77,7 @@ RecordT = TypeVar("RecordT", bound=BaseModel)
 
 class PaginatedResponse(BaseModel, Generic[RecordT]):
     """Generic paginated response wrapper."""
+
     records: list[RecordT]
     total: int
     page: int
@@ -82,6 +91,7 @@ PaginatedSumRecords = PaginatedResponse[SumRecordResponse]
 
 class ProfileResponse(BaseModel):
     """Response model for profile data."""
+
     contact_email: str | None
     telegram: str | None
     signal: str | None
@@ -91,6 +101,7 @@ class ProfileResponse(BaseModel):
 
 class ProfileUpdate(BaseModel):
     """Request model for updating profile."""
+
     contact_email: str | None = None
     telegram: str | None = None
     signal: str | None = None
@@ -99,6 +110,7 @@ class ProfileUpdate(BaseModel):
 
 class InviteCheckResponse(BaseModel):
     """Response for invite check endpoint."""
+
     valid: bool
     status: str | None = None
     error: str | None = None
@@ -106,11 +118,13 @@ class InviteCheckResponse(BaseModel):
 
 class InviteCreate(BaseModel):
     """Request model for creating an invite."""
+
     godfather_id: int
 
 
 class InviteResponse(BaseModel):
     """Response model for invite data (admin view)."""
+
     id: int
     identifier: str
     godfather_id: int
@@ -125,6 +139,7 @@ class InviteResponse(BaseModel):
 
 class UserInviteResponse(BaseModel):
     """Response model for a user's invite (simpler than admin view)."""
+
     id: int
     identifier: str
     status: str
@@ -138,6 +153,7 @@ PaginatedInviteRecords = PaginatedResponse[InviteResponse]
 
 class AdminUserResponse(BaseModel):
     """Minimal user info for admin dropdowns."""
+
     id: int
     email: str
 
@@ -146,11 +162,13 @@ class AdminUserResponse(BaseModel):
 # Availability Schemas
 # =============================================================================
 
+
 class TimeSlot(BaseModel):
     """A single time slot (start and end time)."""
+
     start_time: time
     end_time: time
-    
+
     @field_validator("start_time", "end_time")
     @classmethod
     def validate_15min_boundary(cls, v: time) -> time:
@@ -164,23 +182,27 @@ class TimeSlot(BaseModel):
 
 class AvailabilityDay(BaseModel):
     """Availability for a single day."""
+
     date: date
     slots: list[TimeSlot]
 
 
 class AvailabilityResponse(BaseModel):
     """Response model for availability query."""
+
     days: list[AvailabilityDay]
 
 
 class SetAvailabilityRequest(BaseModel):
     """Request to set availability for a specific date."""
+
     date: date
     slots: list[TimeSlot]
 
 
 class CopyAvailabilityRequest(BaseModel):
     """Request to copy availability from one day to others."""
+
     source_date: date
     target_dates: list[date]
 
@@ -189,20 +211,24 @@ class CopyAvailabilityRequest(BaseModel):
 # Booking Schemas
 # =============================================================================
 
+
 class BookableSlot(BaseModel):
     """A bookable 15-minute slot."""
+
     start_time: datetime
     end_time: datetime
 
 
 class AvailableSlotsResponse(BaseModel):
     """Response for available slots on a given date."""
+
     date: date
     slots: list[BookableSlot]
 
 
 class BookingRequest(BaseModel):
     """Request to book an appointment."""
+
     slot_start: datetime
     note: str | None = None
 
@@ -216,6 +242,7 @@ class BookingRequest(BaseModel):
 
 class AppointmentResponse(BaseModel):
     """Response model for an appointment."""
+
     id: int
     user_id: int
     user_email: str
@@ -234,8 +261,10 @@ PaginatedAppointments = PaginatedResponse[AppointmentResponse]
 # Meta/Constants Schemas
 # =============================================================================
 
+
 class ConstantsResponse(BaseModel):
     """Response model for shared constants."""
+
     permissions: list[str]
     roles: list[str]
     invite_statuses: list[str]