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/app/models/protocol.py

@@ -44,6 +44,7 @@ class VotingProtocol(Base):
     description: Mapped[str | None] = mapped_column(Text)
     vote_type: Mapped[str] = mapped_column(String(32), nullable=False)  # binary, nuanced
     formula_config_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("formula_configs.id"), nullable=False)
+    organization_id: Mapped[uuid.UUID | None] = mapped_column(ForeignKey("organizations.id"), nullable=True, index=True)
     mode_params: Mapped[str | None] = mapped_column(String(64))  # e.g. "D30M50B.1G.2T.1"
     is_meta_governed: Mapped[bool] = mapped_column(Boolean, default=False)
     created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())