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/handlers/import_duty_schedule.py

@@ -1,6 +1,7 @@
 """Import duty-schedule: /import_duty_schedule (admin only). Two steps: handover time -> JSON file."""
 
 import asyncio
+import logging
 
 import duty_teller.config as config
 from telegram import Update
@@ -16,6 +17,8 @@ from duty_teller.importers.duty_schedule import (
 from duty_teller.services.import_service import run_import
 from duty_teller.utils.handover import parse_handover_time
 
+logger = logging.getLogger(__name__)
+
 
 async def import_duty_schedule_cmd(
     update: Update, context: ContextTypes.DEFAULT_TYPE
@@ -80,9 +83,10 @@ async def handle_duty_schedule_document(
     try:
         result = parse_duty_schedule(raw)
     except DutyScheduleParseError as e:
+        logger.warning("Duty schedule parse error: %s", e, exc_info=True)
         context.user_data.pop("awaiting_duty_schedule_file", None)
         context.user_data.pop("handover_utc_time", None)
-        await update.message.reply_text(t(lang, "import.parse_error", error=str(e)))
+        await update.message.reply_text(t(lang, "import.parse_error_generic"))
         return
 
     def run_import_with_scope():
@@ -95,7 +99,8 @@ async def handle_duty_schedule_document(
             None, run_import_with_scope
         )
     except Exception as e:
-        await update.message.reply_text(t(lang, "import.import_error", error=str(e)))
+        logger.exception("Import failed: %s", e)
+        await update.message.reply_text(t(lang, "import.import_error_generic"))
     else:
         total = num_duty + num_unavailable + num_vacation
         unavailable_suffix = (