feat(graph): continual-learning graph data model + dark-Bauhaus viz

Adds the team_model graph layer (the "it learned" view) and its visualization,
per docs/graph.md. Demo-backed first; built on origin/main conventions.

- shared: PodGraph / node / edge / metric types + GraphNodeDoc / GraphEdgeDoc
- backend/src/graph: demo graph data; Mongo store (loadPodGraph w/ demo
  fallback, seedGraph, reachFrom via $graphLookup); graph:seed script
- backend/src/server.ts: additive GET /api/pods/:id/graph + /graph/reach/:node
- frontend: dark-Bauhaus GraphView + fetch helper, reachable from a
  "Team memory" toggle in App.tsx
- docs/graph.md: spec (data model, $graphLookup, API, demo-first plan)

Demo-backed: the route serves a grounded demo graph when team_model has no
graph yet; graph:seed writes team_model + graph_nodes/graph_edges so the
$graphLookup traversal is real. Swap loadPodGraph to live team_model later.

Known follow-ups before merge: branch is based on 65a0791; origin/main is now
at 1294b84, so this needs a rebase + App.tsx conflict resolution (teammate
rewrote App.tsx with live room view / one-click join).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/graph.ts

@@ -0,0 +1,10 @@
+import type { PodGraph } from '@podman/shared';
+
+const BACKEND_URL = import.meta.env.VITE_BACKEND_URL || 'http://localhost:8787';
+
+/** Fetch a pod's continual-learning graph (team_model view, demo fallback). */
+export async function fetchPodGraph(podId: string): Promise<PodGraph> {
+  const res = await fetch(`${BACKEND_URL}/api/pods/${encodeURIComponent(podId)}/graph`);
+  if (!res.ok) throw new Error(`graph request failed: ${res.status}`);
+  return res.json() as Promise<PodGraph>;
+}