Multi-tenancy : espaces de travail + fix auth reload (rate limiter OPTIONS)

- Modèles Organization + OrgMember, migration Alembic (SQLite compatible)
- organization_id nullable sur Document, Decision, Mandate, VotingProtocol
- Service, schéma, router /organizations + dependency get_active_org_id
- Seed : Duniter G1 + Axiom Team ; tout le contenu seed attaché à Duniter G1
- Backend : list/create filtrés par header X-Organization
- Frontend : store organizations, WorkspaceSelector réel, useApi injecte l'org
- Fix critique : rate_limiter exclut les requêtes OPTIONS (CORS preflight)
  → résout le bug "Failed to fetch /auth/me" au reload (429 sur preflight)

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

backend/alembic/versions/2026_04_23_1227-70914b334cfb_add_organizations.py

@@ -0,0 +1,41 @@
+"""add organizations
+
+Revision ID: 70914b334cfb
+Revises:
+Create Date: 2026-04-23 12:27:56.220214+00:00
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = '70914b334cfb'
+down_revision: Union[str, None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # SQLite does not support ADD CONSTRAINT via ALTER TABLE — FK constraints
+    # are declared in models only; integrity is enforced at app layer.
+    op.add_column('decisions', sa.Column('organization_id', sa.Uuid(), nullable=True))
+    op.create_index(op.f('ix_decisions_organization_id'), 'decisions', ['organization_id'], unique=False)
+    op.add_column('documents', sa.Column('organization_id', sa.Uuid(), nullable=True))
+    op.create_index(op.f('ix_documents_organization_id'), 'documents', ['organization_id'], unique=False)
+    op.add_column('mandates', sa.Column('organization_id', sa.Uuid(), nullable=True))
+    op.create_index(op.f('ix_mandates_organization_id'), 'mandates', ['organization_id'], unique=False)
+    op.add_column('voting_protocols', sa.Column('organization_id', sa.Uuid(), nullable=True))
+    op.create_index(op.f('ix_voting_protocols_organization_id'), 'voting_protocols', ['organization_id'], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f('ix_voting_protocols_organization_id'), table_name='voting_protocols')
+    op.drop_column('voting_protocols', 'organization_id')
+    op.drop_index(op.f('ix_mandates_organization_id'), table_name='mandates')
+    op.drop_column('mandates', 'organization_id')
+    op.drop_index(op.f('ix_documents_organization_id'), table_name='documents')
+    op.drop_column('documents', 'organization_id')
+    op.drop_index(op.f('ix_decisions_organization_id'), table_name='decisions')
+    op.drop_column('decisions', 'organization_id')