#677 Progress shows <100% for completed workflows with switch/conditional branches

When workflows use switch operators or conditional branches, unexecuted branches count against progress. Example: ultimate_stress_test_v1 has 24 tasks, but only 22 executed (2 switch branches not taken). Shows 92% despite status=completed. FIX: For terminal states (completed, compensated, failed), always return progress_percentage=100 since the workflow finished its execution path. File: api/blueprints/v1/workflows.py:1530-1539