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>

src/components/panes/DimensionsPane.tsx

@@ -0,0 +1,55 @@
+"use client";
+
+import FolderViewOverlay from '@/components/nodes/FolderViewOverlay';
+import PaneHeader from './PaneHeader';
+import { DimensionsPaneProps, PaneType } from './types';
+
+export default function DimensionsPane({
+  slot,
+  isActive,
+  onPaneAction,
+  onCollapse,
+  onSwapPanes,
+  onNodeOpen,
+  refreshToken,
+  onDataChanged,
+  onDimensionSelect,
+}: DimensionsPaneProps) {
+  const handleTypeChange = (type: PaneType) => {
+    onPaneAction?.({ type: 'switch-pane-type', paneType: type });
+  };
+
+  // When used as a pane, "close" means switch back to node view
+  const handleClose = () => {
+    onPaneAction?.({ type: 'switch-pane-type', paneType: 'node' });
+  };
+
+  return (
+    <div style={{
+      height: '100%',
+      display: 'flex',
+      flexDirection: 'column',
+      background: 'transparent',
+      overflow: 'hidden',
+    }}>
+      <PaneHeader slot={slot} onCollapse={onCollapse} onSwapPanes={onSwapPanes} />
+
+      <div style={{ flex: 1, minHeight: 0, overflow: 'hidden', position: 'relative' }}>
+        {/* FolderViewOverlay expects to be an overlay, so we wrap it in a container */}
+        <div style={{
+          position: 'absolute',
+          inset: 0,
+          background: 'transparent',
+        }}>
+          <FolderViewOverlay
+            onClose={handleClose}
+            onNodeOpen={onNodeOpen}
+            refreshToken={refreshToken}
+            onDataChanged={onDataChanged}
+            onDimensionSelect={onDimensionSelect}
+          />
+        </div>
+      </div>
+    </div>
+  );
+}