feat: Enhance emoji and image management with asynchronous background processing

- Added support for scheduling background tasks to build emoji and image descriptions when not found in cache.
- Improved error handling and logging for emoji and image processing.
- Updated `SessionMessage` processing to allow for optional heavy media analysis and voice transcription.
- Refactored logging messages for better clarity and consistency across various modules.
- Introduced a new function to build outbound log previews for messages, enhancing logging capabilities.

src/common/prompt_i18n.py

@@ -170,7 +170,7 @@ def _format_prompt_template(name: str, template: str, **kwargs: object) -> str:
         error = KeyError(t("prompt.missing_placeholder", name=name, placeholder=missing_placeholder))
         if is_strict_prompt_i18n_mode():
             raise error from exc
-        logger.error("%s", error)
+        logger.error(f"{error}")
         return template
     except Exception as exc:
         logger.error(t("prompt.format_failed", name=name, error=exc))