Local conversation library: list, search, rename, tag, delete, export

[YJack0000]

A proper library view for past conversations, on top of the local SQLite store.

Scope

• Conversation list with title, date, duration, participants/speakers, and a snippet.
• Search & filter: full-text (FTS) over transcript + description; filter by date, speaker/person, tag.
• Manage: rename, edit description, add/remove tags, soft-delete (trash) + restore, permanent delete.
• Detail view: full transcript, evaluations, to-dos, linked people.
• Export: single conversation to a portable format (e.g. Markdown / JSON), and the transcript on its own.
• Sort by recent / duration / title.

Acceptance

• A user can find a past conversation by searching its content, rename it, tag it, and export it — all offline.
• Soft-deleted items go to trash and can be restored; permanent delete removes the row and its index entries.

Notes

• Reuse the FTS index from the local SQLite layer.
• Keep updated_at + tombstones intact for the future sync layer.

Part of #10.