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/organization.py

@@ -0,0 +1,42 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import String, Text, Boolean, DateTime, ForeignKey, Uuid, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.database import Base
+
+
+class Organization(Base):
+    __tablename__ = "organizations"
+
+    id: Mapped[uuid.UUID] = mapped_column(Uuid, primary_key=True, default=uuid.uuid4)
+    name: Mapped[str] = mapped_column(String(128), nullable=False)
+    slug: Mapped[str] = mapped_column(String(128), unique=True, nullable=False, index=True)
+    # commune, enterprise, association, collective, basin, intercommunality, community
+    org_type: Mapped[str] = mapped_column(String(64), default="community")
+    # True = all authenticated users see & interact with content (Duniter G1, Axiom Team)
+    # False = membership required
+    is_transparent: Mapped[bool] = mapped_column(Boolean, default=False)
+    color: Mapped[str | None] = mapped_column(String(32))   # CSS color or mood token
+    icon: Mapped[str | None] = mapped_column(String(64))    # lucide icon name
+    description: Mapped[str | None] = mapped_column(Text)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    members: Mapped[list["OrgMember"]] = relationship(
+        back_populates="organization", cascade="all, delete-orphan"
+    )
+
+
+class OrgMember(Base):
+    __tablename__ = "org_members"
+
+    id: Mapped[uuid.UUID] = mapped_column(Uuid, primary_key=True, default=uuid.uuid4)
+    org_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("organizations.id"), nullable=False)
+    identity_id: Mapped[uuid.UUID] = mapped_column(
+        ForeignKey("duniter_identities.id"), nullable=False
+    )
+    role: Mapped[str] = mapped_column(String(32), default="member")  # admin, member, observer
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+
+    organization: Mapped["Organization"] = relationship(back_populates="members")