Week view flexibility: configurable day count, layout, and a CalDAV task list

- Day count (2-10, was fixed at 7) -- 5 days trims the weekend clutter
  without losing the grid format.
- Layout choice: days side by side (original behavior) or stacked
  vertically as full agenda-style sections (reuses _draw_agenda_day,
  same approach _build_today_tomorrow already used for a fixed 2 days).
- Optional task list (CalDAV VTODO collections only -- a plain ICS
  subscription doesn't meaningfully have one) that takes the space of
  one day slot instead of adding an extra one. Same owner-controls-
  their-own-data permission split as calendar sources: only the
  calendar's owner can point a frame's task list at it, but anyone
  linked to the frame can clear it.

Browse-offset paging now moves by N days (was hardcoded to weeks),
identical to the old behavior when days=7. Changing the day count
resets the browse offset, same reasoning as changing views already did.

server/app/templates/frame_calendar.html

@@ -39,6 +39,15 @@
             </select>
           </label>
           <p class="sub" style="margin-top: 4px;">Only affects the Week and Month views.</p>
+          <label>Days to show (Week view)
+            <input type="number" id="calendar_week_days" min="2" max="10" value="{{ frame.calendar_week_days }}">
+          </label>
+          <label>Week view layout
+            <select id="calendar_week_layout">
+              <option value="horizontal" {% if frame.calendar_week_layout == "horizontal" %}selected{% endif %}>Days side by side</option>
+              <option value="vertical" {% if frame.calendar_week_layout == "vertical" %}selected{% endif %}>Days stacked</option>
+            </select>
+          </label>
           <div class="checkbox-row" id="calendar-inlay-row">
             <input type="checkbox" id="calendar_photo_inlay" {% if frame.calendar_photo_inlay %}checked{% endif %}>
             <label for="calendar_photo_inlay">Show a photo alongside the calendar</label>
@@ -131,6 +140,42 @@
           <button type="button" class="btn-inline" id="weather-city-add">Add</button>
         </div>
       </section>
+
+      <section class="card" style="margin-top: 20px;">
+        <h2 class="card-title">Tasks</h2>
+        <p class="sub">Week view only -- takes the place of one day slot
+          instead of adding an extra one.</p>
+        <div class="checkbox-row" id="tasks-enabled-row">
+          <input type="checkbox" id="tasks_enabled" {% if frame.calendar_tasks_enabled %}checked{% endif %}>
+          <label for="tasks_enabled">Show a task list</label>
+        </div>
+
+        {% if tasks_source %}
+          <p class="sub" style="margin-top: 10px;">
+            Currently using <strong>{{ tasks_source.display_name }}</strong>'s
+            <strong>{{ tasks_source.label }}</strong> list.
+            <button type="button" class="btn-inline secondary" id="tasks-source-clear">Clear</button>
+          </p>
+        {% endif %}
+
+        {% if viewer_task_calendars %}
+          <p class="sub" style="margin-top: 10px;">Use one of your own CalDAV task lists:</p>
+          <ul class="calendar-user-list">
+            {% for c in viewer_task_calendars %}
+              <li class="checkbox-row" style="margin-top: 6px;">
+                <input type="radio" name="tasks-source-choice" class="tasks-source-choice" data-key="{{ c.key }}"
+                       {% if tasks_source and tasks_source.user_id == user.id and frame.calendar_tasks_calendar_key == c.key %}checked{% endif %}>
+                <label style="margin: 0; font-weight: normal;">{{ c.label }}</label>
+              </li>
+            {% endfor %}
+          </ul>
+        {% else %}
+          <p class="sub" style="margin-top: 10px;">You don't have any CalDAV
+            task lists available -- set up a CalDAV account in
+            <a href="/settings">Settings</a> first (a plain ICS subscription
+            doesn't carry tasks).</p>
+        {% endif %}
+      </section>
     </div>
 
     <div class="side-col">