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/schemas/organization.py

@@ -0,0 +1,42 @@
+"""Pydantic v2 schemas for organizations."""
+
+from __future__ import annotations
+
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel, ConfigDict
+
+
+class OrganizationOut(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    name: str
+    slug: str
+    org_type: str
+    is_transparent: bool
+    color: str | None
+    icon: str | None
+    description: str | None
+    created_at: datetime
+
+
+class OrganizationCreate(BaseModel):
+    name: str
+    slug: str
+    org_type: str = "community"
+    is_transparent: bool = False
+    color: str | None = None
+    icon: str | None = None
+    description: str | None = None
+
+
+class OrgMemberOut(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: uuid.UUID
+    org_id: uuid.UUID
+    identity_id: uuid.UUID
+    role: str
+    created_at: datetime