docs: NextGraph multi-user data model — stores, auth matrix, inbox fork plan

Capture the multi-user design exploration as project knowledge + briefs:
- knowledge: NextGraph store types/permissions (+ inbox at protocol, SDK
  exposure, local repo path); integration model (iframe, where the verifier
  runs, generic JS plumbing, ngd stateful, build-time broker target)
- briefs: multi-store refactor; authorization matrix + query inventory +
  derived store partitions; temporary fork to expose the inbox (3 layers:
  SDK fork, Coolify self-hosting, Festipod integration; libs via build:ng)
- fix stale @ng-org versions (alpha.11 -> alpha.13) and a broken
  decision-record link in data-layer.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.project/knowledge/data-layer.md

@@ -72,7 +72,7 @@ See [decision record](../decisions/2026-03-17-1800-sparql-delete-for-orm-objects
 - `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.
+See [decision record](../decisions/2026-03-17-1600-private-store-nuri-scope.md) for why.
 
 ## Context Providers