feat(P04): Add IDEATE stage to orchestrator pipeline — IDEATE-16

- Add ideation-agent to STAGE_AGENT_MAP for ideate stage
- Implement ideate case in executeStage() with mechanical ideation,
  config-aware category filtering, idea deduplication, auto-accept,
  and ---ci--- commit with decision block
- Add test verifying ideate position between research and plan in
  STAGE_ORDER
- 542 tests passing

src/types/pipeline.test.ts

@@ -62,4 +62,14 @@ describe("createInitialPipelineState", () => {
     expect(state.started_at).toBeTruthy();
     expect(state.last_updated).toBeTruthy();
   });
+});
+
+describe("STAGE_ORDER ideate position", () => {
+  it("places ideate between research and plan", () => {
+    const ideateIdx = STAGE_ORDER.indexOf("ideate");
+    const researchIdx = STAGE_ORDER.indexOf("research");
+    const planIdx = STAGE_ORDER.indexOf("plan");
+    expect(ideateIdx).toBeGreaterThan(researchIdx);
+    expect(ideateIdx).toBeLessThan(planIdx);
+  });
 });