plugin(collab-buckets): collaborative buckets via relay

End-to-end shared buckets between relay tenants. Bucket metadata + members
sync through new relay routes (collab-buckets, collab-cards, collab-locks);
card content rides the existing inter-tenant encryption hop. Edit locks,
ownership transfer, LWW conflict stashing, undo for local-bucket destructive
actions, "Make collaborative…" upgrade path, and a resilient outbox for
relay-down create attempts. See plugins/collab-buckets/README.md and
TODO.md for the full picture.

Core hooks added so the plugin can integrate without monkey-patching:
- buckets.js context menu: collab-aware rename/color/delete + Members &
  owner / Make collaborative entries
- editor.js dispatches hyprcrd:editor-open / hyprcrd:editor-close for the
  per-card edit-lock heartbeat
- app.js exposes window.state for the plugin's MutationObserver
- index.php POST/PATCH/DELETE on /api/buckets refuse to mutate collab
  buckets directly (must go through the relay)
- Database.php adds buckets.collab_uid column + unique partial index
- import handler now restores color and collab_uid (was silently dropping
  color, which caused the test runner's auto-restore to wipe custom
  bucket colors)
- relay bootstrap creates collab_buckets, collab_bucket_members,
  collab_cards, collab_card_locks tables and prunes tombstones / expired
  locks on every request

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/modules/editor.js

@@ -200,6 +200,8 @@ export function openModal(card = null) {
     currentLine = -1;
     updateActiveLine();
     inpTitle.focus();
+    // Plugins (collab-buckets) hook into this to heartbeat an edit lock
+    window.dispatchEvent(new CustomEvent('hyprcrd:editor-open', { detail: { card } }));
 }
 
 inpTitle.addEventListener('input', updatePreview);
@@ -354,6 +356,7 @@ body.addEventListener('keyup', updateActiveLine);
 window.addEventListener('resize', () => { if (linesVisible) updateGutter(); });
 
 export function closeModal({ animate = true } = {}) {
+    const closingId = state.editingId;
     if (animate) startCloseMorph();
     else clearMorphGhost();
     hideLinkAc();
@@ -366,6 +369,7 @@ export function closeModal({ animate = true } = {}) {
         state._returnToCalendar = false;
         window._openCalendar?.();
     }
+    window.dispatchEvent(new CustomEvent('hyprcrd:editor-close', { detail: { cardId: closingId } }));
 }
 
 function updatePreview() {