fix(workflows): close re-review gaps in the pull round-trip + partial-failure UI

A re-review of eaf5ace surfaced three follow-ups, all in the fixes themselves:

- pull vs an old server: a returned empty `definition` can only mean a server
  predating the definition-in-list field (a real zero-step workflow is rejected
  at apply). Emitting a stepless `[[workflows]]` block would just fail the next
  apply, so `wire_workflow_to_manifest` now warns and skips it instead.
- base_ms/backoff defaults: the pull mapper keyed its default-omission off a
  hardcoded `500` literal. `default_base_ms` is now `pub` + re-exported, and the
  mapper omits whatever equals `default_base_ms()` / `WorkflowBackoff::default()`
  — no drift if a default ever changes.
- dashboard: a run that succeeds with an `on_error = continue` step failure now
  carries a partial-failure note in `run.error` (from the compute_advance
  change); the run-detail view rendered it as a red failure, contradicting the
  green "succeeded" badge. It now renders as a `.notice` (warning) for a
  succeeded run, `.error` only for a failed one.

Verified: fmt + clippy -D warnings clean; 450 lib tests; 5 workflow CLI
journeys (incl. the pull→plan round-trip); dashboard npm run check clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dashboard/src/routes/apps/[slug]/workflows/+page.svelte

@@ -230,7 +230,12 @@
 			<span class="badge st-{detail.run.status}">{detail.run.status}</span>
 		</h3>
 		{#if detail.run.error}
-			<p class="error">{detail.run.error}</p>
+			<!-- A succeeded run can still carry an `error` note when a step failed
+			     under `on_error = continue` — surface it as a warning, not a
+			     red failure, so the green badge and message don't contradict. -->
+			<p class={detail.run.status === 'succeeded' ? 'notice' : 'error'}>
+				{detail.run.error}
+			</p>
 		{/if}
 
 		<h4>DAG</h4>
@@ -341,6 +346,9 @@
 	.error {
 		color: var(--color-danger);
 	}
+	.notice {
+		color: var(--color-warning, var(--text-muted));
+	}
 	.muted {
 		color: var(--text-muted);
 	}