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/theme.js

@@ -96,8 +96,6 @@ function updatePreview() {
     set('--tp-bar-height',    d.barHeight + 'px');
     set('--tp-pad-card',      d.padCard + 'px');
     set('--tp-shadow-card',   shadows[d.shadowCard] || 'none');
-    const scan = $('theme-preview-scan');
-    if (scan) scan.style.display = String(d.scanlines) === '1' ? '' : 'none';
 }
 
 function fillFontSelect(id, value) {
@@ -129,8 +127,6 @@ function syncControlsFromPending() {
         const valEl = $(valId);
         if (valEl) valEl.textContent = v;
     }
-    const scanEl = $('setting-scanlines');
-    if (scanEl) scanEl.classList.toggle('on', String(designPending.scanlines) === '1');
 }
 
 function commitDesign() {
@@ -167,16 +163,6 @@ function initDesignSettings() {
     if (designWired) return;
     designWired = true;
 
-    // Scanlines toggle
-    const scanEl = $('setting-scanlines');
-    const scanRow = scanEl?.closest('.toggle-row');
-    if (scanRow) scanRow.onclick = () => {
-        const nowOn = !scanEl.classList.contains('on');
-        scanEl.classList.toggle('on', nowOn);
-        designPending.scanlines = nowOn ? '1' : '0';
-        commitDesign();
-    };
-
     // Selects
     for (const [id, key] of SELECT_FIELDS) {
         const el = $(id);