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.

docs/config-catalog.md

@@ -815,18 +815,18 @@ export interface Config {
   maxTotalAgents?: number
   /** Items accepted by a single `parallel()`/`pipeline()` call (default 4096). */
   maxItemsPerCall?: number
-  /** vm timeout for the script's initial synchronous slice AND the meta-literal evaluation (default 5000 ms). */
+  /** vm timeout for the initial synchronous slice (inside the worker) AND the host-side meta evaluation (default 5000 ms). */
   syncTimeoutMs?: number
   /**
    * How long after a cancellation an unsettled script may keep running before
-   * it is abandoned and `result` force-settles `cancelled` (default 5000 ms);
-   * also bounds `dispose()`.
+   * the run force-settles `cancelled` and its worker is TERMINATED (default
+   * 5000 ms); also bounds `dispose()`.
    */
   disposeGraceMs?: number
 }
 ```
 
-Source: [`packages/workflow/workflow-vm/src/index.ts:58`](../packages/workflow/workflow-vm/src/index.ts)
+Source: [`packages/workflow/workflow-vm/src/index.ts:69`](../packages/workflow/workflow-vm/src/index.ts)
 
 ## Loadable plugins with no config