M3 graph view: /api/graph + force-directed SVG

- graph blueprint: GET /api/graph resolves note_links to target notes by
  normalized title (owner-scoped, non-trashed, self-excluded) → {nodes, edges}
  of connected notes.
- GraphView: hand-rolled force simulation (repulsion + edge springs + centering,
  cooling over ~400 frames), SVG nodes/edges, click a node to open it (reuses the
  editor with link navigation). Sidebar Graph entry + route; empty state.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

src/thoughtsync/app.py

@@ -10,6 +10,7 @@ from . import __version__
 from .auth import bp as auth_bp
 from .config import Config
 from .db import session_scope
+from .graph import bp as graph_bp
 from .labels import bp as labels_bp
 from .notes import bp as notes_bp
 from .settings import get_public_config, get_setting, load_or_create_secret_key
@@ -33,6 +34,7 @@ def create_app() -> Quart:
     app.register_blueprint(auth_bp)
     app.register_blueprint(notes_bp)
     app.register_blueprint(labels_bp)
+    app.register_blueprint(graph_bp)
     app.register_blueprint(settings_bp)
 
     @app.before_serving