Add timestamped notes: multi-note support, quick-capture hotkey, live saved indicator

Replace the single free-text note per lesson with a list of timestamped
note entries, migrated transparently from the old format. Adds a
floating notes panel on the lesson page with an always-reachable
quick-capture bar (press N to pause and jump in), inline edit/delete,
click-to-seek timestamps, and a live "Saved Xs ago" indicator. Notes
Hub, the study guide export, and the Outline push all updated to
render multiple timestamped notes per lesson.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

templates/notes_hub.html

@@ -167,6 +167,16 @@
             white-space: nowrap;
             flex-shrink: 0;
         }
+        .timestamp-badge {
+            font-size: 0.75em;
+            background: var(--bg-primary);
+            color: var(--text-muted);
+            padding: 2px 8px;
+            border-radius: 3px;
+            border: 1px solid var(--border-color);
+            white-space: nowrap;
+            flex-shrink: 0;
+        }
         .note-card-body {
             white-space: pre-wrap;
             word-break: break-word;
@@ -213,13 +223,16 @@
                     <span class="note-lesson-title">{{ note.lesson_title }}</span>
                     <span class="note-course-name">{{ note.course_name }}</span>
                 </div>
+                {% if note.timestamp_label %}
+                <span class="timestamp-badge">{{ note.timestamp_label }}</span>
+                {% endif %}
                 {% if note.pushed_to_outline %}
                 <span class="outline-badge">Outline</span>
                 {% endif %}
             </div>
-            <div class="note-card-body">{{ note.note }}</div>
+            <div class="note-card-body">{{ note.text }}</div>
             <a class="note-card-link"
-               href="/recent/open?course_path={{ note.course_path | urlencode }}&lesson_path={{ note.lesson_path | urlencode }}">
+               href="/recent/open?course_path={{ note.course_path | urlencode }}&lesson_path={{ note.lesson_path | urlencode }}{% if note.timestamp_seconds is not none %}&t={{ note.timestamp_seconds }}{% endif %}">
                 Open lesson →
             </a>
         </div>