feat: final schema pass — sync 9 schema changes from main repo

- Rename nodes.content → nodes.notes across all services, tools, API routes, and UI
- Add dimensions.icon column support (GET/POST routes, types)
- Add nodes.event_date column (create/update flows, types)
- Drop nodes.type and nodes.is_pinned references
- Drop edges.user_feedback references
- Drop chat_memory_state table (replaced with DROP IF EXISTS in migration)
- Update schema guide files (system/schema.md)
- Add runtime migration block in sqlite-client.ts for existing databases
- Fix MCP tool schemas (external API keeps 'content' param, maps to 'notes' internally)
- Update standalone MCP server (nodeService.js, sqlite-client.js, index.js)
- Update HTTP MCP server (server.js, stdio-server.js)
- Update all extraction tools (paper, website, youtube)
- Update all UI components (FocusPanel, ThreePanelLayout, GridView, ListView, FolderViewOverlay)
- TypeScript: 0 errors

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

apps/mcp-server/stdio-server.js

@@ -288,7 +288,7 @@ server.registerTool(
 
     const payload = {
       title: title.trim(),
-      content: content?.trim() || undefined,
+      notes: content?.trim() || undefined,
       link: link?.trim() || undefined,
       description: description?.trim() || undefined,
       dimensions: normalizedDimensions,
@@ -351,7 +351,7 @@ server.registerTool(
         nodes: nodes.map((node) => ({
           id: node.id,
           title: node.title,
-          content: node.content ?? null,
+          notes: node.notes ?? null,
           description: node.description ?? null,
           link: node.link ?? null,
           dimensions: node.dimensions || [],
@@ -647,7 +647,7 @@ server.registerTool(
         results: results.map(r => ({
           nodeId: r.node_id || r.nodeId || r.id,
           title: r.title || 'Untitled',
-          chunkPreview: (r.chunk || r.content || '').slice(0, 200),
+          chunkPreview: (r.chunk || r.notes || '').slice(0, 200),
           similarity: r.similarity || r.score || 0
         }))
       }