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>

crates/shared/src/lib.rs

@@ -121,6 +121,6 @@ pub use validator::{ScriptValidator, ValidatedScript, ValidationError};
 pub use vars::{NoopVarsService, VarsError, VarsService};
 pub use version::{API_VERSION, PRODUCT_VERSION, SDK_VERSION, WIRE_VERSION};
 pub use workflow::{
-    NoopWorkflowService, OnError, RunStatus, StepStatus, WorkflowBackoff, WorkflowDefinition,
-    WorkflowError, WorkflowRetry, WorkflowService, WorkflowStepDef,
+    default_base_ms, NoopWorkflowService, OnError, RunStatus, StepStatus, WorkflowBackoff,
+    WorkflowDefinition, WorkflowError, WorkflowRetry, WorkflowService, WorkflowStepDef,
 };