docs: describe the workflow engine as worker-thread first

The outer ring catches up with the engine swap (the package's own
README/JSDoc rode the port commit):

- Seam module doc and README name the worker-thread engine as THE
  implementation, with isolated-vm/separate-process sandboxing as the
  deferred hardening; the seam service doc states the holder-owned-runs
  contract (engine-fiber disposal deliberately leaves live runs to
  their holders).
- Seam contract precision: agentsStarted documents the termination-path
  degradation to the host-observed count; the events section scopes the
  agent-start/agent-end pair to calls that STARTED a child run;
  WorkflowRun wording drops the vm-era abandonment language.
- The dynamic-workflows RFC is rewritten in place to the shipped
  mechanism (implemented-RFC rule): why worker threads, the thread's
  concrete buys, the in-process node:vm first cut recorded under
  alternatives considered; the tool section describes the usage policy
  as the tool's own prompt section.
- gen-doc-graphs: six workflow/* DYNAMIC_EVENT_DISPATCHERS entries (the
  catalog no longer claims nothing dispatches them) and the seam-note
  wording; core-data-structures gains its workflow.md index row;
  packages/README + AGENTS.md layout line + example cordis.yml comments
  say worker-thread; catalogs regenerated.

scripts/gen-doc-graphs.ts

@@ -193,7 +193,7 @@ const SERVICE_ROLES: ServiceRole[] = [
     mode: 'seam',
     implementations: ['workflow-vm'],
     consumers: ['tool-workflow'],
-    note: 'One engine per context (bash shape, no named-provider registry); the vm engine fans agent() calls out through ctx.subagents.',
+    note: 'One engine per context (bash shape, no named-provider registry); the worker-thread engine fans agent() calls out through ctx.subagents.',
   },
 ]
 
@@ -203,6 +203,14 @@ const DYNAMIC_EVENT_DISPATCHERS: Array<{ event: string; pkg: string; method: str
   // listeners or strand an already-started child run.
   { event: 'subagent/start', pkg: 'subagent', method: 'events.dispatch' },
   { event: 'subagent/end', pkg: 'subagent', method: 'events.dispatch' },
+  // The workflow/* lifecycle events dispatch the same way, for the same
+  // per-listener-containment reason (WorkflowService.emitWorkflowEvent).
+  { event: 'workflow/start', pkg: 'workflow', method: 'events.dispatch' },
+  { event: 'workflow/phase', pkg: 'workflow', method: 'events.dispatch' },
+  { event: 'workflow/log', pkg: 'workflow', method: 'events.dispatch' },
+  { event: 'workflow/agent-start', pkg: 'workflow', method: 'events.dispatch' },
+  { event: 'workflow/agent-end', pkg: 'workflow', method: 'events.dispatch' },
+  { event: 'workflow/end', pkg: 'workflow', method: 'events.dispatch' },
 ]
 
 function generatedHeader(title: string): string[] {