fix: narrow parse and prefetch exception handling

[fmueller]

Summary

• replace broad parse-time except Exception blocks in note/body loaders with targeted parser exceptions (yaml.YAMLError, TypeError, ValueError)
• tighten translation prefetch fallback handling to catch expected runtime failures (RuntimeError, PostEditAborted) instead of swallowing all exceptions
• reduce language detection fallback catches to targeted runtime/value/type/attribute failure classes
• add regression tests for loader parse error mapping and for preserving unexpected prefetch exceptions

Validation

• uv run ruff check
• uv run mypy
• uv run pytest