Graph-view round 1 (owner): full-bleed canvas — no padding, under the floating chrome

The home graph view had breathing room on every side (main px-4 py-2,
the composer docked below in flow, the header above). Per the owner:

- The canvas now owns the whole column — absolute inset-0, from the
  sidebar to the right edge of the screen, bottom to top, zero padding.
- The header floats over the graph (pointer-events-none except the
  sidebar toggle, so the canvas stays draggable around it).
- The new-session blob + stats bar dock OVER the graph at the bottom,
  no gradient scrims anywhere — the graph runs clean under everything
  to the very edges.
- The renderer itself is untouched: same canvas, same data, same fit
  logic — only its container grew. The composer keeps chat's DOCK
  geometry (max-w-[46rem] px-4) so nothing shifts when a session starts.

Verified live in headless chromium (1280×800, sidebar open): canvas
spans x 288→1280 (sidebar edge → right edge), y 0→800 (bottom to top);
the header overlays the top; the dock overlays the bottom with its
content ending 16px above the viewport edge.

package-lock.json

@@ -27,7 +27,9 @@
 				"cmdk": "^1.1.1",
 				"d3-force": "^3.0.0",
 				"d3-selection": "^3.0.0",
+				"d3-shape": "^3.2.0",
 				"d3-zoom": "^3.0.0",
+				"dagre-d3-es": "7.0.14",
 				"embla-carousel-react": "^8.6.0",
 				"katex": "^0.16.47",
 				"linkedom": "^0.18.13",