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/config.py

@@ -1,7 +1,8 @@
 """Load configuration from environment (e.g. .env via python-dotenv).
 
 BOT_TOKEN is not validated on import; call require_bot_token() in the entry point
-when running the bot.
+when running the bot. Numeric env vars (HTTP_PORT, INIT_DATA_MAX_AGE_SECONDS) use
+safe parsing with defaults on invalid values.
 """
 
 import logging
@@ -16,6 +17,11 @@ from duty_teller.i18n.lang import normalize_lang
 
 load_dotenv()
 
+logger = logging.getLogger(__name__)
+
+# Valid port range for HTTP_PORT.
+HTTP_PORT_MIN, HTTP_PORT_MAX = 1, 65535
+
 # Project root (parent of duty_teller package). Used for webapp path, etc.
 PROJECT_ROOT = Path(__file__).resolve().parent.parent
 
@@ -55,6 +61,48 @@ def _normalize_log_level(raw: str) -> str:
     return "INFO"
 
 
+def _parse_int_env(
+    name: str, default: int, min_val: int | None = None, max_val: int | None = None
+) -> int:
+    """Parse an integer from os.environ; use default on invalid or out-of-range. Log on fallback."""
+    raw = os.getenv(name)
+    if raw is None or raw == "":
+        return default
+    try:
+        value = int(raw.strip())
+    except ValueError:
+        logger.warning(
+            "Invalid %s=%r (expected integer); using default %s",
+            name,
+            raw,
+            default,
+        )
+        return default
+    if min_val is not None and value < min_val:
+        logger.warning(
+            "%s=%s is below minimum %s; using %s", name, value, min_val, min_val
+        )
+        return min_val
+    if max_val is not None and value > max_val:
+        logger.warning(
+            "%s=%s is above maximum %s; using %s", name, value, max_val, max_val
+        )
+        return max_val
+    return value
+
+
+def _validate_database_url(url: str) -> bool:
+    """Return True if URL looks like a supported SQLAlchemy URL (sqlite or postgres)."""
+    if not url or not isinstance(url, str):
+        return False
+    u = url.strip().split("?", 1)[0].lower()
+    return (
+        u.startswith("sqlite://")
+        or u.startswith("postgresql://")
+        or u.startswith("postgres://")
+    )
+
+
 @dataclass(frozen=True)
 class Settings:
     """Injectable settings built from environment. Used in tests or when env is overridden."""
@@ -105,20 +153,30 @@ class Settings:
         raw_host = (os.getenv("HTTP_HOST") or "127.0.0.1").strip()
         http_host = raw_host if raw_host else "127.0.0.1"
         bot_username = (os.getenv("BOT_USERNAME", "") or "").strip().lstrip("@").lower()
+        database_url = os.getenv("DATABASE_URL", "sqlite:///data/duty_teller.db")
+        if not _validate_database_url(database_url):
+            logger.warning(
+                "DATABASE_URL does not look like a supported URL (sqlite:// or postgresql://); "
+                "DB connection may fail."
+            )
+        http_port = _parse_int_env(
+            "HTTP_PORT", 8080, min_val=HTTP_PORT_MIN, max_val=HTTP_PORT_MAX
+        )
+        init_data_max_age = _parse_int_env("INIT_DATA_MAX_AGE_SECONDS", 0, min_val=0)
         return cls(
             bot_token=bot_token,
-            database_url=os.getenv("DATABASE_URL", "sqlite:///data/duty_teller.db"),
+            database_url=database_url,
             bot_username=bot_username,
             mini_app_base_url=os.getenv("MINI_APP_BASE_URL", "").rstrip("/"),
             http_host=http_host,
-            http_port=int(os.getenv("HTTP_PORT", "8080")),
+            http_port=http_port,
             allowed_usernames=allowed,
             admin_usernames=admin,
             allowed_phones=allowed_phones,
             admin_phones=admin_phones,
             mini_app_skip_auth=os.getenv("MINI_APP_SKIP_AUTH", "").strip()
             in ("1", "true", "yes"),
-            init_data_max_age_seconds=int(os.getenv("INIT_DATA_MAX_AGE_SECONDS", "0")),
+            init_data_max_age_seconds=init_data_max_age,
             cors_origins=cors,
             external_calendar_ics_url=os.getenv(
                 "EXTERNAL_CALENDAR_ICS_URL", ""