refactor(orchestrator): running status, queue cap, loader to lib/agent

Review follow-ups on the queue and loader:
- TaskStatus 'in_progress' -> 'running' (drop the snake_case outlier)
- inline the nowIso() one-liner
- document that dependsOn is a DAG by construction (ids point only at
  earlier tasks), so cycles cannot form
- cap the queue at 30 tasks as a runaway backstop; real sizing rests on
  agent/skill design
- move agent-prompt-loader from programs/orchestrator/ to lib/agent/

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: gewenyu99

src/lib/programs/orchestrator/__tests__/agent-prompt-loader.test.ts

@@ -57,6 +57,18 @@ describe('checkEnqueueGuards', () => {
     const r = checkEnqueueGuards(ctx, { type: 'init', reason: 'x' });
     expect(r).toEqual({ ok: true });
   });
+
+  it('refuses to grow the queue past the runaway cap', () => {
+    for (let i = 0; i < 30; i++) {
+      store.enqueue({ type: 'capture', inputs: { i } });
+    }
+    const r = checkEnqueueGuards(ctx, {
+      type: 'init',
+      inputs: { i: 30 },
+      reason: 'x',
+    });
+    expect(r).toMatchObject({ ok: false, guard: 'queue-full' });
+  });
 });
 
 describe('apply functions', () => {