fix: delete a sticky note on close instead of only hiding it

[itzmekhokan]

Summary

Fixes #344.

The sticky-note title-bar × was labelled "Hide sticky note" and only called layer.forget() — an in-memory eviction. The backing wp_guideline post was never touched, so the note reappeared on the next heartbeat tick, page reload, or any desktop re-render. Since the × was the only removal affordance, a note could never actually be deleted.

Fix

Make the × delete the note, following the same soft-trash + Undo pattern the desktop-files layer (trashPlacementWithUndo) already uses:

• rest.ts — add deleteStickyNote() (REST trash, not force, so it stays recoverable) and restoreStickyNote() (untrash by flipping status back to private). fetchStickyNotes only queries status: 'private', so a trashed note never re-hydrates onto the desktop.
• layer.ts — the × now trashes the note with optimistic eviction and an Undo toast, and is relabelled "Delete sticky note". A dismissedIds guard drops any in-flight heartbeat/reload echo for a just-deleted id so it can't resurrect the note before the trash propagates.
• A note created and closed inside the save debounce is persisted first (save() now hands callers its in-flight promise) so there's always a server row to trash — closing the create-then-delete race behind the intermittent resurrection.

No behaviour change for the "empty, never-saved note" case (still dropped locally with no round-trip).

Testing

• npm run typecheck, npm run lint — clean
• npm run test:js — 1610 pass (adds 2 tests: the × trashes + evicts the note, and a stale heartbeat echo can't re-add a deleted note)
• Manual, in wp-env:
  • Clicking × deletes the note and shows a "…deleted" toast with Undo; the wp_guideline post moves to trash.
  • The note no longer returns after a full page reload (the Closing a sticky note doesn't delete it — the note reappears on the next desktop render #344 repro) — verified 0 notes and the post staying trash.
  • Undo / restoreStickyNote flips the post back to private and re-adds the note.

[AllTerrainDeveloper]

Hey Thanks for your contribution! I'll ask the person who made the Sticky Notes, not sure if he really intended to hide for the session or close them forever. @artpi?

[AllTerrainDeveloper]

I'll reach Artur internally 😆