feat: v6.3.0 API publique complete v2 (REST /api/v2, scopes, OpenAPI)

- Router api_v2.py (~100 endpoints) : tokens, users, workspaces/members,
  collections, pages, proprietes, vues/dashboards, commentaires/mentions,
  notifications, favoris/tags/recents, partage/publish, historique, sprints,
  templates, export/import, forges, recherche FTS, admin, webhooks CRUD
- Helpers api_v2_helpers.py : Bearer unifie (sha256/expires_at/extension_devices),
  scopes hierarchiques read<write<admin, pagination + X-Total-Count, ISO-8601,
  RFC 7807, idempotence, audit, rate-limit par token
- Migration 20 : api_tokens.scopes/expires_at, webhook_deliveries,
  api_audit_log, idempotency_keys
- main.py : handler d'erreurs unifie StarletteHTTPException, /docs + /redoc
- config : PUBLIC_API_INSECURE_OK (dev only), API_V2_RATE_LIMIT_PER_TOKEN
- OpenAPI docs/openapi-v2.json (402 chemins), tests/test_public_api_v2.py (24)
- Docs : CHANGELOG (v6.2.0/6.2.1 clipper + v6.3.0), ROADMAP, API_GUIDE_V6,
  V6_Web_Clipper, README, ARCHITECTURE, /help
- Suite complete 668 verte, ruff OK

tests/conftest.py

@@ -26,6 +26,7 @@ def client():
     os.environ["DATABASE_URL"] = f"sqlite:///{db_path}"
     os.environ["APP_SECRET_KEY"] = "test-secret-for-tests"
     os.environ["RATE_LIMIT_ENABLED"] = "false"
+    os.environ["PUBLIC_API_INSECURE_OK"] = "true"
     os.environ["BACKUP_ENABLED"] = "true"
     os.environ["BACKUP_DIR"] = backup_dir
     os.environ["PROJECT_SYNC_ENABLED"] = "false"
@@ -43,6 +44,7 @@ def client():
     s.database_url = f"sqlite:///{db_path}"
     s.app_secret_key = "test-secret-for-tests"
     s.rate_limit_enabled = False
+    s.public_api_insecure_ok = True
     s.backup_enabled = True
     s.backup_dir = backup_dir
     s.backup_interval_hours = 24