feat(nav): timetable view toggle (By Class / By Term), fix cc-section-node crash

- Fix: skip canvas navigation for Section-type nodes (was crashing on cc-section-node)
- Add By Class / By Term toggle to My Timetable section (mirrors calendar Generic/Academic)
- By Class: pre-loaded SubjectClass children shown immediately on expand
- By Term: lazy-loads AcademicTerms -> Weeks -> TaughtLessons when switched to term view
- displayChildren respects timetableView context for the timetable section

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

src/utils/tldraw/ui-overrides/components/shared/navigation/CCGraphNavPanel.tsx

@@ -102,6 +102,10 @@ interface NavPanelContextValue {
     onSetupTimetable: () => void;
     onOnboardSchool: () => void;
     activeNodeId?: string;
+    timetableView: 'class' | 'term';
+    setTimetableView: (v: 'class' | 'term') => void;
+    timetableTermNodes: TreeNode[];
+    timetableTermStatus: 'idle' | 'loading' | 'populated' | 'empty';
 }
 
 const NavPanelContext = createContext<NavPanelContextValue>({
@@ -113,6 +117,10 @@ const NavPanelContext = createContext<NavPanelContextValue>({
     onSetupSchoolCalendar: () => {},
     onSetupTimetable: () => {},
     onOnboardSchool: () => {},
+    timetableView: 'class',
+    setTimetableView: () => {},
+    timetableTermNodes: [],
+    timetableTermStatus: 'idle',
 });
 
 // ─── TreeItem ─────────────────────────────────────────────────────────────────
@@ -150,7 +158,9 @@ function TreeItem({ node, depth, onSelect, onExpand }: TreeItemProps) {
 
     const displayChildren = isCalendarSection && ctx.calendarMode === 'academic'
         ? ctx.academicTerms
-        : children;
+        : isTimetableSection && ctx.timetableView === 'term'
+            ? ctx.timetableTermNodes
+            : children;
 
     const academicEmpty = isCalendarSection
         && ctx.calendarMode === 'academic'
@@ -349,6 +359,34 @@ function TreeItem({ node, depth, onSelect, onExpand }: TreeItemProps) {
                     )}
                 </Box>
 
+                {/* Timetable view toggle */}
+                {isTimetableSection && node.status === 'populated' && (
+                    <Box sx={{ px: 1.5, pb: 0.5 }}>
+                        <ToggleButtonGroup
+                            value={ctx.timetableView}
+                            exclusive
+                            onChange={(_, v) => { if (v) ctx.setTimetableView(v); }}
+                            size="small"
+                            sx={{ height: 22 }}
+                        >
+                            <ToggleButton value="class" sx={{ px: 1, fontSize: '0.6rem', textTransform: 'none' }}>
+                                By Class
+                            </ToggleButton>
+                            <ToggleButton value="term" sx={{ px: 1, fontSize: '0.6rem', textTransform: 'none' }}>
+                                By Term
+                            </ToggleButton>
+                        </ToggleButtonGroup>
+                        {ctx.timetableView === 'term' && ctx.timetableTermStatus === 'loading' && (
+                            <CircularProgress size={10} sx={{ mt: 0.5, ml: 0.5 }} />
+                        )}
+                        {ctx.timetableView === 'term' && ctx.timetableTermStatus === 'empty' && (
+                            <Typography variant="caption" sx={{ display: 'block', color: 'text.disabled', fontSize: '0.6rem', mt: 0.5 }}>
+                                No academic calendar linked to timetable
+                            </Typography>
+                        )}
+                    </Box>
+                )}
+
                 {/* Calendar mode toggle */}
                 {isCalendarSection && (
                     <Box sx={{ px: 1.5, pb: 0.5 }}>
@@ -377,7 +415,10 @@ function TreeItem({ node, depth, onSelect, onExpand }: TreeItemProps) {
                     </Box>
                 )}
 
-                {(canExpand || (isCalendarSection && ctx.calendarMode === 'academic' && displayChildren.length > 0)) && (
+                {(canExpand
+                    || (isCalendarSection && ctx.calendarMode === 'academic' && displayChildren.length > 0)
+                    || (isTimetableSection && ctx.timetableView === 'term' && displayChildren.length > 0)
+) && (
                     <Collapse in={expanded} timeout="auto">
                         {displayChildren.map(child => (
                             <TreeItem key={child.neo4j_node_id} node={child} depth={depth + 1}
@@ -452,6 +493,11 @@ export function CCGraphNavPanel() {
     const [calendarMode, setCalendarMode] = useState<CalendarMode>('generic');
     const [academicCalendarStatus, setAcademicCalendarStatus] = useState<NavPanelContextValue['academicCalendarStatus']>('idle');
     const [academicTerms, setAcademicTerms] = useState<TreeNode[]>([]);
+    const [timetableView, setTimetableView] = useState<'class' | 'term'>('class');
+    const [timetableTermNodes, setTimetableTermNodes] = useState<TreeNode[]>([]);
+    const [timetableTermStatus, setTimetableTermStatus] = useState<'idle' | 'loading' | 'populated' | 'empty'>('idle');
+    const [timetableNodeId, setTimetableNodeId] = useState<string | undefined>();
+    const [timetableDb, setTimetableDb] = useState<string | undefined>();
 
     const [calendarWizardOpen, setCalendarWizardOpen] = useState(false);
     const [timetableWizardOpen, setTimetableWizardOpen] = useState(false);
@@ -497,10 +543,41 @@ export function CCGraphNavPanel() {
         if (accessToken && !tree) fetchTree();
     }, [accessToken, tree, fetchTree]);
 
+    useEffect(() => {
+        if (!tree) return;
+        const ttSection = tree.children?.find(n => n.section_id === 'timetable');
+        if (ttSection && ttSection.node_type === 'TeacherTimetable') {
+            setTimetableNodeId(ttSection.neo4j_node_id);
+            setTimetableDb(ttSection.neo4j_db_name);
+        }
+    }, [tree]);
+
     useEffect(() => {
         if (accessToken && !schoolStatus) fetchSchoolStatus();
     }, [accessToken, schoolStatus, fetchSchoolStatus]);
 
+    // Fetch timetable term nodes when switching to term view
+    useEffect(() => {
+        if (timetableView !== 'term' || !timetableNodeId || !timetableDb || !accessToken) return;
+        if (timetableTermStatus !== 'idle') return;
+        setTimetableTermStatus('loading');
+        const params = new URLSearchParams({
+            neo4j_node_id: timetableNodeId,
+            neo4j_db_name: timetableDb,
+            node_type: 'TeacherTimetable',
+            section_id: 'timetable-term',
+        });
+        fetch(`${apiBase}/graph/node/children?${params}`, {
+            headers: { Authorization: `Bearer ${accessToken}` },
+        })
+            .then(r => r.json())
+            .then(data => {
+                setTimetableTermNodes(data.children || []);
+                setTimetableTermStatus(data.children?.length > 0 ? 'populated' : 'empty');
+            })
+            .catch(() => setTimetableTermStatus('empty'));
+    }, [timetableView, timetableNodeId, timetableDb, accessToken, apiBase, timetableTermStatus]);
+
     // Fetch academic calendar when switching to academic mode
     useEffect(() => {
         if (calendarMode !== 'academic' || !accessToken) return;
@@ -547,7 +624,9 @@ export function CCGraphNavPanel() {
     }, [accessToken, apiBase]);
 
     const handleSelect = useCallback((node: TreeNode) => {
-        if (!node.is_section || node.neo4j_node_id) navigateToNeoNode(node);
+        // Section nodes with artificial IDs (node_type="Section") have no canvas shape util
+        if (node.is_section && node.node_type === "Section") return;
+        navigateToNeoNode(node);
     }, [navigateToNeoNode]);
 
     const refreshAll = useCallback(() => {
@@ -595,6 +674,10 @@ export function CCGraphNavPanel() {
         onSetupTimetable: () => setTimetableWizardOpen(true),
         onOnboardSchool: () => setOnboardingWizardOpen(true),
         activeNodeId,
+        timetableView,
+        setTimetableView: (v) => { setTimetableView(v); if (v === 'class') { setTimetableTermStatus('idle'); setTimetableTermNodes([]); } },
+        timetableTermNodes,
+        timetableTermStatus,
     };
 
     const defaultSchoolInfo: SchoolInfo = {