feat(audit): P1 cross-tenant/RBAC tests, P3 test fixes, P2/P3 frontend fixes

- P1-Tests: 12 test files with new cross-tenant isolation + RBAC tests
- P3-Tests: 8 fixes (duplicate fixtures, sys.path.insert, unused imports, KeyError)
- P3-Frontend: LucideIcons → ICON_MAP (2 files), inline styles → Tailwind (2 files)
- P3-Frontend: DOMPurify for iframe XSS, redundant regex removed, console.log → console.debug
- P2-Frontend: 2 notification API TODOs retained (requires larger refactor)
- conftest.py: create_no_perm_user helper added
- pyproject.toml: pythonpath for scripts/ added
- All checks green: ruff 0, F821 0, tsc 0, app 495 routes, cross-plugin 0

tests/test_custom_fields.py

@@ -162,3 +162,50 @@ class TestCustomFieldDefinition:
         )
         assert len(manifest.custom_fields) == 1
         assert manifest.custom_fields[0].name == "score"
+
+
+# ── Cross-tenant isolation test ──
+@pytest.mark.asyncio
+class TestCustomFieldsCrossTenant:
+    """Custom fields must not leak across tenants."""
+
+    async def test_cross_tenant_isolation(self, client: AsyncClient, db_session):
+        """Tenant B cannot access custom fields of tenant A's contact."""
+        from httpx import ASGITransport
+        from httpx import AsyncClient as AC
+
+        import app.main
+
+        await seed_tenant_and_users(db_session)
+        await login_client(client, "admin@tenanta.com")
+        # Create a contact in tenant A
+        create_resp = await client.post(
+            "/api/v1/contacts",
+            json={"type": "company", "name": "Tenant A Custom Corp", "displayname": "Tenant A Custom Corp"},
+            headers=ORIGIN_HEADER,
+        )
+        assert create_resp.status_code == 201
+        contact_id = create_resp.json()["id"]
+
+        # Tenant B admin must not access tenant A's contact custom fields
+        app_instance = app.main.app
+        async with AC(transport=ASGITransport(app=app_instance), base_url="http://test") as client_b:
+            await login_client(client_b, "admin@tenantb.com")
+            resp = await client_b.get(
+                f"/api/v1/contacts/{contact_id}/custom-fields",
+                headers=ORIGIN_HEADER,
+            )
+            assert resp.status_code == 404
+
+    async def test_rbac_no_permission(self, client: AsyncClient, db_session):
+        """User without contacts:read permission gets 403 on GET custom fields."""
+        from tests.conftest import create_no_perm_user
+
+        seed = await seed_tenant_and_users(db_session)
+        await create_no_perm_user(db_session, seed)
+        await login_client(client, "noperm@tenanta.com")
+        resp = await client.get(
+            "/api/v1/contacts/00000000-0000-0000-0000-000000000000/custom-fields",
+            headers=ORIGIN_HEADER,
+        )
+        assert resp.status_code == 403