Improve handling of unreadable entries (BAD_DECRYPT)

[Doccrazy]

Unreadable/corrupt items can occur on undetected merge conflicts or when manually editing repository files. Example:

1. You create a new entry but do not push immediately
2. Another user updates authorization info for the folder, causing the folder key to change
3. You pull and merge (no conflict as different files are affected)

Currently, this error is not handled, issuing a BAD_DECRYPT error toast, leaving the entry unreadable and the full text search completely broken. Worse, the error message does not point to the affected entry so the user has a hard time fixing it manually.

Improvements:

• Skip unreadable entries in fulltext search, issue error but do not abort completely
• Show more helpful error message
• Offer mitigation options (delete entry, recover from previous commit)