feat: node view redesign — single-scroll, no tabs

Ports the full node view redesign from ra-h. Replaces the 4-tab layout
(Desc/Notes/Edges/Source) with a single-scroll document view.

- New FocusPanel: frontmatter rows, collapse toggle, NodeSearchModal,
  TipTap SourceEditor, section headers with extending rules
- NodeSearchModal: new full-screen portal modal for creating connections
- SourceEditor: TipTap WYSIWYG editor (new file)
- SourceReader: removed header chrome, added onContentClick prop
- Source formatters: inherit font, 15px/1.7, no max-width centering
- DimensionTags: subtle dashed + button replaces green pill
- autoEmbedQueue: recover nodes stuck in 'chunking' state on startup
- edges: fix extra parameter in getNodeConnectionsSQLite

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

package.json

@@ -26,6 +26,8 @@
     "@langchain/core": "^1.0.1",
     "@langchain/textsplitters": "^1.0.1",
     "@modelcontextprotocol/sdk": "^1.25.3",
+    "@tiptap/react": "^3.20.4",
+    "@tiptap/starter-kit": "^3.20.4",
     "@xyflow/react": "^12.10.0",
     "ai": "^6.0.27",
     "better-sqlite3": "^12.2.0",
@@ -40,6 +42,7 @@
     "react-dom": "^19.0.1",
     "react-markdown": "^10.1.0",
     "remark-gfm": "^4.0.1",
+    "tiptap-markdown": "^0.9.0",
     "youtube-transcript": "^1.2.1",
     "youtube-transcript-plus": "^1.1.1",
     "zod": "^3.25.76"