Fix NextGraph write persistence: use private_store_id as useShape scope

Writes (doc_create, orm_frontend_update) failed with RepoNotFound because
useShape with did:ng:i scope doesn't open individual repos in the verifier's
cache. Switched to did🆖${session.private_store_id} as both scope and
@graph, matching the expense-tracker-rdf pattern. This opens the private
store repo via orm_start_graph, making it available for subsequent writes.

Also adds wallet login step to ensureAuth so the verifier bootstraps repos
from the remote broker into localStorage on first run.

Key changes:
- useShapeWithDefaults accepts storeNuri param (private store NURI)
- FestipodDataContext.useNgData() passes private store scope
- ensureGraphNuri() simplified: reuse existing @graph or private_store_id
- ngBootstrap uses ensureGraphNuri + flushAndWait between ORM adds
- harness-ng.tsx uses private store scope for test bridge shapes
- hooks.ts: wallet creation logs in to bootstrap verifier repos
- E2e steps for data loading and persistence verification

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

.project/knowledge/data-layer.md

@@ -35,6 +35,25 @@ ORM bindings in `src/shared/shapes/orm/`:
 
 Regenerate with `bun run build:orm`.
 
+## NextGraph Read/Write Pattern
+
+The app follows the same pattern as the official expense-tracker-rdf example:
+
+- **Scope**: `useShape(shapeType, `did:ng:${session.private_store_id}`)` — opens the private store repo in the verifier
+- **@graph**: `did:ng:${session.private_store_id}` — writes target the same NURI
+
+This is critical: `orm_start_graph` with the private store NURI explicitly opens the repo in the verifier's `self.repos` HashMap. Without this, `orm_frontend_update` fails with `RepoNotFound`.
+
+**Do NOT use `did:ng:i` as scope** — it subscribes to the entire user site via a special code path that doesn't open individual repos, breaking all writes.
+
+### Key files
+
+- `src/shared/hooks/useShapeWithDefaults.ts` — Accepts `storeNuri` param, passes to `useShape`
+- `src/shared/utils/ngGraph.ts` — `ensureGraphNuri()` returns `@graph` for entity creation
+- `src/shared/utils/ngBootstrap.ts` — Seeds test data using `ensureGraphNuri()` for `@graph`
+
+See [decision record](.project/decisions/2026-03-17-1600-private-store-nuri-scope.md) for why.
+
 ## Context Providers
 
 ### NextGraphContext (`src/shared/context/NextGraphContext.tsx`)