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/alembic/versions/2026_04_23_1900-c4e812fb3a01_add_groups.py

@@ -0,0 +1,51 @@
+"""Add groups and group_members tables.
+
+Revision ID: c4e812fb3a01
+Revises: b78571ae9e00
+Create Date: 2026-04-23 19:00:00.000000
+"""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "c4e812fb3a01"
+down_revision = "b78571ae9e00"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "groups",
+        sa.Column("id", sa.Uuid(), nullable=False),
+        sa.Column("name", sa.String(128), nullable=False),
+        sa.Column("description", sa.Text(), nullable=True),
+        sa.Column("organization_id", sa.Uuid(), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.Column("updated_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.ForeignKeyConstraint(["organization_id"], ["organizations.id"]),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("ix_groups_organization_id", "groups", ["organization_id"])
+
+    op.create_table(
+        "group_members",
+        sa.Column("id", sa.Uuid(), nullable=False),
+        sa.Column("group_id", sa.Uuid(), nullable=False),
+        sa.Column("identity_id", sa.Uuid(), nullable=True),
+        sa.Column("display_name", sa.String(128), nullable=False),
+        sa.Column("added_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+        sa.ForeignKeyConstraint(["group_id"], ["groups.id"]),
+        sa.ForeignKeyConstraint(["identity_id"], ["duniter_identities.id"]),
+        sa.PrimaryKeyConstraint("id"),
+    )
+    op.create_index("ix_group_members_group_id", "group_members", ["group_id"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_group_members_group_id", table_name="group_members")
+    op.drop_table("group_members")
+    op.drop_index("ix_groups_organization_id", table_name="groups")
+    op.drop_table("groups")