#178 DSL Test 3: Parallel Branches Workflow

PROMPT: Create a workflow with 3 parallel branches that each run a different shell command, then wait for all to complete and print a summary. EXPECTED: builder.parallel() with 3 branches, tools.workflow.wait_for_parallel_branches to wait, result_key on parallel, summary task with dependencies. VALIDATION: All 3 branches execute concurrently, wait completes, summary runs.