feat: enhance error handling and configuration validation

- Added a global exception handler to log unhandled exceptions and return a generic 500 JSON response without exposing details to the client.
- Updated the configuration to validate the `DATABASE_URL` format, ensuring it starts with `sqlite://` or `postgresql://`, and log warnings for invalid formats.
- Introduced safe parsing for numeric environment variables (`HTTP_PORT`, `INIT_DATA_MAX_AGE_SECONDS`) with defaults on invalid values, including logging warnings for out-of-range values.
- Enhanced the duty schedule parser to enforce limits on the number of schedule rows and the length of full names and duty strings, raising appropriate errors when exceeded.
- Updated internationalization messages to include generic error responses for import failures and parsing issues, improving user experience.
- Added unit tests to verify the new error handling and configuration validation behaviors.

duty_teller/services/import_service.py

@@ -1,5 +1,6 @@
 """Import duty schedule: delete range, insert duties/unavailable/vacation. Accepts session."""
 
+import logging
 from datetime import date, timedelta
 
 from sqlalchemy.orm import Session
@@ -14,6 +15,8 @@ from duty_teller.db.repository import (
 from duty_teller.importers.duty_schedule import DutyScheduleResult
 from duty_teller.utils.dates import day_start_iso, day_end_iso, duty_to_iso
 
+logger = logging.getLogger(__name__)
+
 
 def _consecutive_date_ranges(dates: list[date]) -> list[tuple[date, date]]:
     """Sort dates and merge consecutive ones into (first, last) ranges. Empty list -> []."""
@@ -53,16 +56,24 @@ def run_import(
     Returns:
         Tuple (num_users, num_duty, num_unavailable, num_vacation).
     """
+    logger.info(
+        "Import started: range %s..%s, %d entries",
+        result.start_date,
+        result.end_date,
+        len(result.entries),
+    )
     from_date_str = result.start_date.isoformat()
     to_date_str = result.end_date.isoformat()
     num_duty = num_unavailable = num_vacation = 0
 
-    # Batch: get all users by full_name, create missing
+    # Batch: get all users by full_name, create missing (no commit until end)
     names = [e.full_name for e in result.entries]
     users_map = get_users_by_full_names(session, names)
     for name in names:
         if name not in users_map:
-            users_map[name] = get_or_create_user_by_full_name(session, name)
+            users_map[name] = get_or_create_user_by_full_name(
+                session, name, commit=False
+            )
 
     # Delete range per user (no commit)
     for entry in result.entries:
@@ -113,4 +124,11 @@ def run_import(
         session.bulk_insert_mappings(Duty, duty_rows)
     session.commit()
     invalidate_duty_related_caches()
+    logger.info(
+        "Import done: %d users, %d duty, %d unavailable, %d vacation",
+        len(result.entries),
+        num_duty,
+        num_unavailable,
+        num_vacation,
+    )
     return (len(result.entries), num_duty, num_unavailable, num_vacation)