collab attachments, multi-day events, calendar improvements

- Collab buckets sync attachments alongside cards (images/PDFs/audio).
  New /api/collab-attachments endpoint on relay, encrypted at rest,
  bucket-scoped for members.
- CalDAV multi-day events via **Bis:** body field. Calendar renders
  event on every day in range with day counter (1/6, 2/6, ...).
- Calendar preserves month across close/reopen (only jumps to today
  on first open).
- Calendar title: centered nav group with [MM-DD] Mon Y [KW-KW] —
  dimmed brackets, fixed width so nothing wiggles.
- Editor: scratchpad uses custom confirm, autobackup-draft dialog
  replaced with custom styled dialog.
- Scanlines theme feature removed (performance issue).

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

public/js/modules/editor.js

@@ -4,6 +4,7 @@ import { $, esc, api, escRe, getCsrf, fuzzyMatch } from './util.js';
 import { state, getChildren, CARD_COLORS } from './state.js';
 import { renderMd, addCodeCopyButtons, formatTodoItems } from './markdown.js';
 import { pushCardEdit, snapshotCard } from './undo.js';
+import { showDialog } from './dialog.js';
 
 const modal = $('modal');
 const body = $('editor-body');
@@ -238,7 +239,7 @@ export function openModal(card = null) {
     updateActiveLine();
 
     // Check for unsaved draft (newer than what we just loaded).
-    // Skipped during test runs — tests would block on the confirm dialog.
+    // Skipped during test runs — tests would block on the dialog.
     const draft = loadDraft(card?.id);
     if (draft && !window._testRunning) {
         const cardModified = card ? Date.parse(card.updated_at + 'Z') || 0 : 0;
@@ -248,18 +249,27 @@ export function openModal(card = null) {
         if (draftIsNewer && draftHasContent && differsFromLoaded) {
             const age = Math.round((Date.now() - draft.savedAt) / 60000);
             const ageText = age < 1 ? 'just now' : age < 60 ? `${age} min ago` : `${Math.round(age / 60)} h ago`;
-            const restore = window.confirm(`Unsaved draft from ${ageText} found.\n\nRestore it?`);
-            if (restore) {
-                inpTitle.value = draft.title || '';
-                body.value = draft.body || '';
-                if (scratchpadBody) scratchpadBody.value = draft.scratchpad || '';
-                updatePreview();
-            } else {
-                clearDraft(card?.id);
-            }
+            const cardId = card?.id;
+            // Async confirm — fires after openModal returns
+            (async () => {
+                const restore = await showDialog({
+                    title: 'unsaved draft',
+                    message: `Unsaved draft from ${ageText} found.\n\nRestore it?`,
+                    okLabel: 'Restore',
+                    cancelLabel: 'Discard',
+                });
+                if (!modal.classList.contains('open') || state.editingId != cardId) return;
+                if (restore) {
+                    inpTitle.value = draft.title || '';
+                    body.value = draft.body || '';
+                    if (scratchpadBody) scratchpadBody.value = draft.scratchpad || '';
+                    updatePreview();
+                } else {
+                    clearDraft(cardId);
+                }
+            })();
         }
     } else if (draft && window._testRunning) {
-        // During tests, silently discard any draft so it doesn't accumulate
         clearDraft(card?.id);
     }