[pending-judge] feat(DC-161): calendar widget + Radicale auto-wiring

- Top-bar calendar widget (status/js/calendar-widget.js): next-appointment
  display, settings modal with CalDAV/ICS source management and a
  Test-connection probe. Follows the weather-widget pattern.
- Backend routes/calendar.js: sources CRUD (secrets in credential manager,
  never in responses), aggregated events across sources with per-source
  error isolation, Radicale provision endpoint, CalDAV discover probe.
- src/calendar/ics-parser.js: dependency-free RFC 5545 parser with bounded
  RRULE expansion (DAILY/WEEKLY-BYDAY/MONTHLY/YEARLY, COUNT/UNTIL/INTERVAL,
  EXDATE consumes COUNT, RECURRENCE-ID overrides), 500-event cap.
- src/calendar/caldav-client.js: CalDAV REPORT time-range queries over
  node:https (no new deps), HTTPS-enforced off localhost, 5MiB response cap.
- src/calendar/radicale-provisioner.js: zero-config auto-wiring - generates
  a 24-char password, writes Radicale htpasswd config (pure-Node APR1 hash
  verified byte-for-byte against openssl passwd -apr1 vectors), stores
  credentials, registers the source. Deploy hook in routes/apps/deploy.js
  wires any Radicale deployed via the App Selector automatically.
- Radicale app template (tomsquest/docker-radicale) in the catalog.
- Tests: 32 new (parser unit, provisioner unit incl. openssl vectors,
  route tests). Full suite 3552 passed; only pre-existing pdf-parse
  billing/invoice failures remain (proven red at base 448f535).
- OpenAPI: 5 calendar paths documented. CHANGELOG entry added.

status/index.html

@@ -132,6 +132,15 @@
             <button id="clock-settings" class="clock-settings-btn" aria-label="Clock settings">⚙️</button>
           </div>
         </div>
+
+        <!-- Calendar widget (DC-161) — auto-wires to DashCaddy-deployed Radicale -->
+        <div class="calendar-widget-container">
+          <div id="calendar-widget" class="calendar-widget" title="Calendar — click for details" role="button" tabindex="0" aria-label="Calendar widget">
+            <div class="calendar-widget-icon">📅</div>
+            <span class="calendar-widget-text">Calendar</span>
+            <button id="calendar-settings" class="weather-settings-btn-bottom" aria-label="Calendar settings">⚙️</button>
+          </div>
+        </div>
       </div>
 
       <!-- License status + Reload Caddy Button - top right corner -->