feat(super-productivity): sync task notes to Super Productivity

[BigWebstas]

Description

Syncs task notes between Parallel Code and Super Productivity for tasks linked to a Super Productivity task. Until now only the title was synced.

• Parallel Code to Super Productivity: editing a linked task's notes sends them to Super Productivity after a 500 ms debounce. A new SuperProductivityUpdateTaskNotes IPC channel handles the send.
• Super Productivity to Parallel Code: when a linked task is focused, the notes are read alongside the title and merged.
• Merge rule: a three-way merge against the last notes both sides agreed on (syncedNotes, persisted with the link).
  • Whichever side changed wins.
  • If both changed, Parallel Code wins.
  • On a freshly linked task with no base, Super Productivity's notes are pulled only when Parallel Code's are empty.
• New tasks from Super Productivity start with that task's notes.
• Notes longer than 100,000 characters are shortened before sending, without splitting a surrogate pair.

Issues Resolved

None filed.

Check List

• New functionality includes testing. (Merge rules, client and store sync tests.)
• New functionality has been documented in the README if applicable. (Not applicable: the existing Super Productivity integration has no notes section.)

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