Groupes d'identités : modèle DB, router, store, UI cercles + Protocoles

- Group + GroupMember : modèle SQLAlchemy + migration + router CRUD
- /api/v1/groups : liste, création, suppression, membres (add/remove)
- groups.ts : store Pinia (fetchAll, getGroup, create, remove, addMember, removeMember)
- decisions/new.vue : cercles 1 & 2 en mode texte libre OU groupe prédéfini
  (affected_count calculé depuis le member_count du groupe)
- protocols/index.vue : section Groupes avec expand/collapse, ajout/suppression membres
- lang="fr" + spellcheck sur tous les textareas ; placeholder cercle 2 corrigé
- n8n channels : prévu sprint futur (texte libre → webhook appel à contribution)

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

backend/app/schemas/group.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict
+
+
+class GroupMemberCreate(BaseModel):
+    display_name: str
+    identity_id: uuid.UUID | None = None
+
+
+class GroupMemberOut(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    display_name: str
+    identity_id: uuid.UUID | None
+    added_at: datetime
+
+
+class GroupCreate(BaseModel):
+    name: str
+    description: str | None = None
+
+
+class GroupOut(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    name: str
+    description: str | None
+    organization_id: uuid.UUID | None
+    created_at: datetime
+    members: list[GroupMemberOut] = []
+
+
+class GroupSummary(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    name: str
+    description: str | None
+    organization_id: uuid.UUID | None
+    member_count: int = 0