Empty note close does not reliably delete note

[ComputelessComputer]

Closing an empty note tab does not reliably delete the backing session.

Also reproduces when closing the currently active tab, not just other close flows.

Likely cause: isSessionEmpty(...) in apps/desktop/src/store/tinybase/store/sessions.ts determines editor emptiness by serializing TipTap JSON to markdown with json2md(...). Some visually blank editor states serialize as non-empty strings, for example:

• empty paragraph ->  
• empty bullet list -> -  
• empty task list -> - [ ]  

The current logic only special-cases  , so blank notes in empty list/task-list states are treated as non-empty and skipped by close-tab cleanup.

Expected:
Closing a visually empty note should consistently delete it regardless of its empty TipTap structure.

Suggested fix:
Use TipTap structural emptiness checks (isEmptyTiptapContent(...)) on parsed JSON instead of markdown serialization for the primary emptiness gate, with string fallback only for legacy raw content.