Add test coverage for workflows router endpoints

[reo0603]

Summary

• Add missing test coverage for workflows router endpoints (DELETE, GET executions)
• Add authenticated endpoint tests for enable/disable/executions

Motivation

Workflows router had 4 endpoints but incomplete test coverage:

• DELETE /api/workflows/{id} - zero tests
• GET /api/workflows/{id}/executions - zero tests
• POST /api/workflows/{id}/enable - only auth test, missing authenticated test

All other routers have comprehensive test coverage following the pattern: auth enforcement tests + authenticated endpoint tests.

Changes

Added 4 new tests:

• test_workflow_executions_requires_auth - auth enforcement for executions endpoint
• test_workflow_enable_authenticated - authenticated test (404 on missing workflow)
• test_workflow_disable_authenticated - authenticated test for DELETE endpoint
• test_workflow_executions_authenticated - authenticated test for executions endpoint

Testing

Tests follow the same pattern as other routers:

• Auth enforcement tests verify 401 without credentials
• Authenticated tests verify proper error handling (404 for nonexistent workflows)

[Lightheartdevs]

Clean PR — the 4 new tests are correct and follow the existing patterns in the file.

Minor observations (non-blocking):

1. Pre-existing docstring bug (not introduced by this PR): test_workflow_disable_requires_auth (line 55) has docstring POST /api/workflows/{id}/disable but the actual route is DELETE /api/workflows/{id} and the test correctly uses test_client.delete. The new test_workflow_disable_authenticated gets this right. Consider fixing the old docstring in a follow-up.

2. Coverage gap to be aware of: The 3 authenticated tests only exercise the 404 "workflow not in catalog" path. The happy paths for enable/disable/executions all require a live n8n connection, so testing them would need aiohttp mocking (the mock_aiohttp_session fixture in conftest.py exists for this). Not a blocker for this PR since it's explicitly filling the auth + 404 gaps, but worth noting for future work.

No CLAUDE.md violations, no bugs, no security issues. LGTM.