sync: Major UI updates from private repo (Jan 16-24)

Features synced:
- UI Panels Refactor: flexible pane system with ChatPane, NodePane,
  DimensionsPane, WorkflowsPane, ViewsPane, MapPane
- Source Content Reader: content type detection + 4 formatters
  (transcript, book, markdown, raw)
- Source Content Search: Cmd+F search in Source Reader
- Feed Layout Overhaul: LeftToolbar, SplitHandle, CollapsedRail
- Map Panel: promoted to first-class pane
- Edge policy simplification: auto-inference + direction correction

New files:
- src/components/panes/* (pane system)
- src/components/layout/CollapsedRail.tsx
- src/components/layout/LeftToolbar.tsx
- src/components/layout/SplitHandle.tsx
- src/components/focus/source/* (Source Reader + formatters)
- src/components/views/ViewsOverlay.tsx

Updated:
- ThreePanelLayout.tsx (complete refactor)
- FocusPanel.tsx (Source tab integration)
- API routes (dimensions GET, edges auto-inference)
- Database services (nodes, edges, dimensions)

Dependencies added:
- react-markdown
- remark-gfm

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/dimensions/route.ts

@@ -5,6 +5,45 @@ import { DimensionService } from '@/services/database/dimensionService';
 
 export const runtime = 'nodejs';
 
+export async function GET() {
+  try {
+    const sqlite = getSQLiteClient();
+
+    // Get all dimensions with their counts
+    const result = sqlite.query(`
+      WITH dimension_counts AS (
+        SELECT nd.dimension, COUNT(*) AS count
+        FROM node_dimensions nd
+        GROUP BY nd.dimension
+      )
+      SELECT
+        d.name AS dimension,
+        d.description,
+        d.is_priority AS isPriority,
+        COALESCE(dc.count, 0) AS count
+      FROM dimensions d
+      LEFT JOIN dimension_counts dc ON dc.dimension = d.name
+      ORDER BY d.is_priority DESC, d.name ASC
+    `);
+
+    return NextResponse.json({
+      success: true,
+      data: result.rows.map((row: any) => ({
+        dimension: row.dimension,
+        description: row.description,
+        isPriority: Boolean(row.isPriority),
+        count: Number(row.count)
+      }))
+    });
+  } catch (error) {
+    console.error('Error fetching dimensions:', error);
+    return NextResponse.json({
+      success: false,
+      error: 'Failed to fetch dimensions'
+    }, { status: 500 });
+  }
+}
+
 export async function POST(request: NextRequest) {
   try {
     const body = await request.json();

app/api/edges/route.ts

@@ -27,10 +27,10 @@ export async function POST(request: NextRequest) {
     const body = await request.json();
     
     // Validate required fields
-    if (!body.from_node_id || !body.to_node_id || typeof body.explanation !== 'string') {
+    if (!body.from_node_id || !body.to_node_id) {
       return NextResponse.json({
         success: false,
-        error: 'Missing required fields: from_node_id, to_node_id, and explanation are required'
+        error: 'Missing required fields: from_node_id and to_node_id are required'
       }, { status: 400 });
     }
 
@@ -57,15 +57,9 @@ export async function POST(request: NextRequest) {
 
     const fromId = parseInt(body.from_node_id);
     const toId = parseInt(body.to_node_id);
+    // Explanation can be empty - service will auto-generate
     const explanation = String(body.explanation || '').trim();
 
-    if (!explanation) {
-      return NextResponse.json({
-        success: false,
-        error: 'explanation is required and cannot be empty'
-      }, { status: 400 });
-    }
-
     const skipInference = Boolean(body.skip_inference);
     const createdVia = (() => {
       const raw = typeof body.created_via === 'string' ? body.created_via : '';