feat(notes): liens internes, onglet Réseau, living blocks et consentement IA

Rend les liens entre notes visibles et persistants (sync NoteLink au save, auto-save, graphe réseau rafraîchi), ajoute living blocks, Memory Echo, recherche globale, consentement IA explicite et consolide les prototypes design en architectural-grid.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/sprint-status.yaml

@@ -1,5 +1,5 @@
 # generated: 2026-05-14T16:06:50Z
-# last_updated: 2026-05-16T21:00:00Z
+# last_updated: 2026-05-23T14:25:15Z
 # project: Momento
 # project_key: NOKEY
 # tracking_system: file-system
@@ -35,7 +35,7 @@
 # - Dev moves story to 'review', then runs code-review (fresh context, different LLM recommended)
 
 generated: 2026-05-14T16:06:50Z
-last_updated: 2026-05-16T21:00:00Z
+last_updated: 2026-05-23T20:03:48Z
 project: Momento
 project_key: NOKEY
 tracking_system: file-system
@@ -47,14 +47,14 @@ development_status:
   3-2-custom-llm-router: done
   3-3-smart-routing-fallback: done
   3-4-host-pays-session-logic: done
-  3-5-secure-byok-management: review
-  3-6-stripe-subscription-tiers: review
+  3-5-secure-byok-management: done
+  3-6-stripe-subscription-tiers: done
   epic-3-retrospective: optional
   epic-4: in-progress
   4-1-gdpr-cookie-consent: done
   4-2-gdpr-right-to-be-forgotten: done
-  4-3-data-portability: backlog
-  4-4-explicit-ai-consent: backlog
+  4-3-data-portability: done
+  4-4-explicit-ai-consent: done
   4-5-eu-data-residency: backlog
   4-6-sso-saml-audit-logging: backlog
   epic-4-retrospective: optional