fix: return 404 on deploy/stop for non-existent workflow IDs

[Copilot]

The deploy and stop pipeline routes were performing an UPDATE then returning steps.get-workflow.row unconditionally — when the workflow ID didn't exist, db_query (mode: single) returned found: false with an empty row, causing a 200 {} response instead of a 404.

Changes

• Both /deploy and /stop pipelines: added check-exists (step.db_query) + check-found (step.conditional) before the UPDATE, consistent with the PUT/DELETE workflow route pattern
• If the workflow is not found, the pipeline short-circuits to a not-found step returning 404 {"error": "workflow not found"}
• The UPDATE is skipped entirely for non-existent IDs

- name: check-exists
  type: step.db_query
  config:
    database: admin-db
    query: "SELECT id FROM workflows WHERE id = ?"
    params: ["{{index .steps \"parse-request\" \"path_params\" \"id\"}}"]
    mode: single
- name: check-found
  type: step.conditional
  config:
    field: "steps.check-exists.found"
    routes:
      "false": not-found
    default: set-now
# ... activate/deactivate, get-workflow, respond ...
- name: not-found
  type: step.json_response
  config:
    status: 404
    body:
      error: "workflow not found"

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