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/models/group.py

@@ -0,0 +1,41 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import String, Text, DateTime, ForeignKey, Uuid, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.database import Base
+
+
+class Group(Base):
+    __tablename__ = "groups"
+
+    id: Mapped[uuid.UUID] = mapped_column(Uuid, primary_key=True, default=uuid.uuid4)
+    name: Mapped[str] = mapped_column(String(128), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text)
+    organization_id: Mapped[uuid.UUID | None] = mapped_column(
+        ForeignKey("organizations.id"), nullable=True, index=True
+    )
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+    members: Mapped[list["GroupMember"]] = relationship(
+        back_populates="group", cascade="all, delete-orphan"
+    )
+
+
+class GroupMember(Base):
+    __tablename__ = "group_members"
+
+    id: Mapped[uuid.UUID] = mapped_column(Uuid, primary_key=True, default=uuid.uuid4)
+    group_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("groups.id"), nullable=False, index=True)
+    # FK to duniter_identities when the member is a known WoT member; nullable for free-text entries
+    identity_id: Mapped[uuid.UUID | None] = mapped_column(
+        ForeignKey("duniter_identities.id"), nullable=True
+    )
+    display_name: Mapped[str] = mapped_column(String(128), nullable=False)
+    added_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    group: Mapped["Group"] = relationship(back_populates="members")