Planner UX improvements and grading max-points display

- Today button jumps planner to current week; today column highlighted with accent outline
- Week label now shows friendly format (Aug 3–7, 2026) instead of ISO dates
- Course color shown as left border on scheduled course items
- Parent-side done toggle on every planner task (works for offline + course items)
- Within-day drag-to-reorder tasks via new /api/schedule/reorder endpoint
- Grading queue shows visible "/ N pts" max-points label (defaults to 100 when unset)
- New item default points changed from 10 to 100

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/admin.html

@@ -334,6 +334,7 @@
           <button id="planner-prev" class="secondary">← Prev</button>
           <span id="planner-week-label" class="week-label"></span>
           <button id="planner-next" class="secondary">Next →</button>
+          <button id="planner-today" class="secondary">Today</button>
           <button id="planner-copy" class="secondary">Copy last week</button>
           <button id="planner-print">🖨 Print</button>
           <button id="planner-add-btn">+ Add task</button>