feat: update check (#561)

feat(update-check): add robust update check with interval support, state management, and CLI integration

- Implement version and interval-based update checks with configurable settings
- Add CLI command `kleinanzeigen-bot update-check` for manual checks
- Introduce state file with versioning, UTC timestamps, and migration logic
- Validate and normalize intervals (1d–4w) with fallback for invalid values
- Ensure correct handling of timezones and elapsed checks
- Improve error handling, logging, and internationalization (i18n)
- Add comprehensive test coverage for config, interval logic, migration, and CLI
- Align default config, translations, and schema with new functionality
- Improve help command UX by avoiding config/log loading for `--help`
- Update documentation and README with full feature overview

src/kleinanzeigen_bot/model/config_model.py

@@ -9,6 +9,7 @@ from typing import Annotated, Any, List, Literal
 from pydantic import AfterValidator, Field, model_validator
 from typing_extensions import deprecated
 
+from kleinanzeigen_bot.model.update_check_model import UpdateCheckConfig
 from kleinanzeigen_bot.utils import dicts
 from kleinanzeigen_bot.utils.misc import get_attr
 from kleinanzeigen_bot.utils.pydantics import ContextualModel
@@ -142,6 +143,7 @@ Example:
     browser:BrowserConfig = Field(default_factory = BrowserConfig, description = "Browser configuration")
     login:LoginConfig = Field(default_factory = LoginConfig.model_construct, description = "Login credentials")
     captcha:CaptchaConfig = Field(default_factory = CaptchaConfig)
+    update_check:UpdateCheckConfig = Field(default_factory = UpdateCheckConfig, description = "Update check configuration")
 
     def with_values(self, values:dict[str, Any]) -> Config:
         return Config.model_validate(