feat(data): activate isolation — declare identity + connections to the SDK

Festipod performs the domain acts that make isolation real: AccountContext
declares the current identity at login/change; FestipodDataContext declares its
connections (friendships) to the data SDK. Reads then discriminate by scope
through the SDK (private→owner, protected→owner+connections, public→all) — no
app-side filtering, no store ids, no awareness that isolation is emulated. New
@data scenario proves an unconnected account can't read another's protected
entity but can after connecting; public stays visible. @data 21/21.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.project/concepts/functional-domain/_debt.md

@@ -0,0 +1,9 @@
+# Doc-debt — functional-domain
+
+> Presence of a block = doc to update. Processed → delete the block; no blocks left → delete this file.
+> One block = one "big change": `why` + `files` + `verify` (leaves to review).
+
+## Block: T03.b — l'isolation par périmètre est désormais ACTIVE (confirmatoire)
+- **why**: Le modèle produit public/protected/private (knowledge_data-scopes-and-discovery) devient effectivement appliqué : protected = propriétaire + connexions, public = tous, private = propriétaire. Le fait DOMAINE (les connexions) est déclaré au SDK par l'app ; le contenu doctrinal du périmètre est inchangé (le code converge vers la doctrine, ne l'invalide pas). Le fichier .feature ne fait que valider ce modèle.
+- **files**: src/modules/workshop/features/protected-connections.feature
+- **verify (leaves à relire)**: knowledge_data-scopes-and-discovery.md — confirmer que le triptyque public/protected/private + "connexions bilatérales" reste exact (aucun changement attendu). Bloc à supprimer après relecture confirmatoire.