chore: remove all dryRun infrastructure

dryRun no longer needed — tests use mock agents + mock fetch instead.
Removes isDryRun from WorkflowFnOptions, dryRun from ExtractConfig,
dryRunMeta from RoleDefinition, --dry-run from CLI, and all related
plumbing in engine/worker/fork/extract.

小橘 <xiaoju@shazhou.work>

examples/hello-world.ts

@@ -27,12 +27,10 @@ const greeter: RoleDefinition<Roles["greeter"]> = {
   description: "Generates a greeting",
   systemPrompt: "You greet the user briefly.",
   schema: greeterMetaSchema,
-  dryRunMeta: { greeting: "Hello!" },
 };
 
 const extract = {
   provider: { baseUrl: "http://127.0.0.1:9", apiKey: "", model: "" },
-  dryRun: true,
 } as const;
 
 export const run = createWorkflow<Roles>(