Add configuration rules, refactor settings management, and enhance import functionality

- Introduced a new configuration file `.cursorrules` to define coding standards, error handling, testing requirements, and project-specific guidelines.
- Refactored `config.py` to implement a `Settings` dataclass for better management of environment variables, improving testability and maintainability.
- Updated the import duty schedule handler to utilize session management with `session_scope`, ensuring proper database session handling.
- Enhanced the import service to streamline the duty schedule import process, improving code organization and readability.
- Added new service layer functions to encapsulate business logic related to group duty pinning and duty schedule imports.
- Updated README documentation to reflect the new configuration structure and improved import functionality.

db/repository.py

@@ -63,14 +63,13 @@ def delete_duties_in_range(
 ) -> int:
     """Delete all duties of the user that overlap [from_date, to_date] (YYYY-MM-DD). Returns count deleted."""
     # start_at < to_date + 1 day so duties starting on to_date are included (start_at is ISO with T)
-    to_next = (datetime.fromisoformat(to_date + "T00:00:00") + timedelta(days=1)).strftime("%Y-%m-%d")
-    q = (
-        session.query(Duty)
-        .filter(
-            Duty.user_id == user_id,
-            Duty.start_at < to_next,
-            Duty.end_at >= from_date,
-        )
+    to_next = (
+        datetime.fromisoformat(to_date + "T00:00:00") + timedelta(days=1)
+    ).strftime("%Y-%m-%d")
+    q = session.query(Duty).filter(
+        Duty.user_id == user_id,
+        Duty.start_at < to_next,
+        Duty.end_at >= from_date,
     )
     count = q.count()
     q.delete(synchronize_session=False)
@@ -89,7 +88,9 @@ def get_duties(
     in UTC (ISO 8601 with Z). Use to_date_next so duties starting on to_date are included
     (start_at like 2025-01-31T09:00:00Z is > "2025-01-31" lexicographically).
     """
-    to_date_next = (datetime.fromisoformat(to_date + "T00:00:00") + timedelta(days=1)).strftime("%Y-%m-%d")
+    to_date_next = (
+        datetime.fromisoformat(to_date + "T00:00:00") + timedelta(days=1)
+    ).strftime("%Y-%m-%d")
     q = (
         session.query(Duty, User.full_name)
         .join(User, Duty.user_id == User.id)
@@ -119,12 +120,11 @@ def insert_duty(
     return duty
 
 
-def get_current_duty(
-    session: Session, at_utc: datetime
-) -> tuple[Duty, User] | None:
+def get_current_duty(session: Session, at_utc: datetime) -> tuple[Duty, User] | None:
     """Return the duty (and user) for which start_at <= at_utc < end_at, event_type='duty'.
     at_utc is in UTC (naive or aware); comparison uses ISO strings."""
     from datetime import timezone
+
     if at_utc.tzinfo is not None:
         at_utc = at_utc.astimezone(timezone.utc)
     now_iso = at_utc.strftime("%Y-%m-%dT%H:%M:%S") + "Z"
@@ -147,6 +147,7 @@ def get_next_shift_end(session: Session, after_utc: datetime) -> datetime | None
     """Return the end_at of the current duty (if after_utc is inside one) or of the next duty.
     For scheduling the next pin update. Returns naive UTC datetime."""
     from datetime import timezone
+
     if after_utc.tzinfo is not None:
         after_utc = after_utc.astimezone(timezone.utc)
     after_iso = after_utc.strftime("%Y-%m-%dT%H:%M:%S") + "Z"
@@ -161,7 +162,9 @@ def get_next_shift_end(session: Session, after_utc: datetime) -> datetime | None
         .first()
     )
     if current:
-        return datetime.fromisoformat(current.end_at.replace("Z", "+00:00")).replace(tzinfo=None)
+        return datetime.fromisoformat(current.end_at.replace("Z", "+00:00")).replace(
+            tzinfo=None
+        )
     # Next future duty: start_at > after_iso, order by start_at
     next_duty = (
         session.query(Duty)
@@ -170,7 +173,9 @@ def get_next_shift_end(session: Session, after_utc: datetime) -> datetime | None
         .first()
     )
     if next_duty:
-        return datetime.fromisoformat(next_duty.end_at.replace("Z", "+00:00")).replace(tzinfo=None)
+        return datetime.fromisoformat(next_duty.end_at.replace("Z", "+00:00")).replace(
+            tzinfo=None
+        )
     return None
 
 
@@ -206,7 +211,9 @@ def get_all_group_duty_pin_chat_ids(session: Session) -> list[int]:
     return [r[0] for r in rows]
 
 
-def set_user_phone(session: Session, telegram_user_id: int, phone: str | None) -> User | None:
+def set_user_phone(
+    session: Session, telegram_user_id: int, phone: str | None
+) -> User | None:
     """Set phone for user by telegram_user_id. Returns User or None if not found."""
     user = session.query(User).filter(User.telegram_user_id == telegram_user_id).first()
     if not user: