feat: persist task creation drafts using scratch storage (Vibe Kanban)

[stunningpixels]

Summary

This PR implements draft persistence for the task creation dialog, allowing users to recover their work if they accidentally close the dialog or navigate away.

Changes Made

Backend (crates/db/src/models/scratch.rs)

• Added new DraftTaskData struct to store task draft information:
  • title: The draft task title
  • description: The draft task description
  • auto_start: Whether to auto-start the task on creation
• Updated ScratchPayload::DraftTask variant to use DraftTaskData instead of a plain String

Type Generation (crates/server/src/bin/generate_types.rs)

• Added DraftTaskData to the list of exported TypeScript types

Frontend (frontend/src/components/dialogs/tasks/TaskFormDialog.tsx)

• Integrated useScratch hook for draft persistence (only in create mode)
• Added debounced auto-save (500ms) for title, description, and auto-start settings
• Load saved drafts when opening the create task dialog
• Clear drafts on successful task creation or when user explicitly discards changes
• Fixed timing issue where form validation failed on page reload due to repoBranches loading asynchronously

Implementation Details

• Draft ID Strategy: Uses the project ID as the scratch key, allowing one draft per project
• Debounced Saves: Uses useDebouncedCallback with 500ms delay to avoid excessive API calls
• Graceful Degradation: If the scratch WebSocket fails to connect, the form still works (just without draft persistence)
• Form Validation Fix: Added useEffect to sync repoBranches field when branches finish loading, ensuring the Create button enables correctly when loading a saved draft

Why These Changes

Users reported losing their task descriptions when accidentally closing the dialog or navigating away. This feature leverages the existing scratch infrastructure (already used for follow-up message drafts) to provide automatic draft saving without requiring explicit user action.

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This PR was written using Vibe Kanban

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[stunningpixels]

Finally jfc

[ggordonhall]

How is this triggered? When you close the task creation dialog you are forced to confirm that you want to discard unsaved changes.

[stunningpixels]

It's from our user in Japan who said sometimes their browser crashes and they lose their work