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/types/database.ts

@@ -64,23 +64,16 @@ export interface Edge {
 
 export type EdgeSource = 'user' | 'ai_similarity' | 'helper_name';
 
-export type EdgeContextCategory = 'attribution' | 'intellectual';
-
 export type EdgeContextType =
-  | 'created_by'
-  | 'features'
-  | 'part_of'
-  | 'source_of'
-  | 'extends'
-  | 'supports'
-  | 'contradicts'
-  | 'related_to';
+  | 'created_by'   // Content → Creator (book by author, podcast by host)
+  | 'part_of'      // Part → Whole (episode of podcast, person discussed in book)
+  | 'source_of'    // Derivative → Source (insight from article)
+  | 'related_to';  // Default — anything else or when unsure
 
 export type EdgeCreatedVia = 'ui' | 'agent' | 'mcp' | 'workflow' | 'quicklink' | 'quick_capture_auto';
 
 export interface EdgeContext {
   // SYSTEM-INFERRED (AI classifies from explanation + nodes)
-  category: EdgeContextCategory;
   type: EdgeContextType;
   confidence: number;   // 0-1
   inferred_at: string;  // ISO timestamp