refactor(P06): rename milestone type schema-breaking → major, reinforce release flow

---ci---
phase: 6
milestone: v0.10
status: execute
decisions:
  - id: D-001
    decision: Rename MilestoneType schema-breaking to major for clarity
    rationale: Major better describes the semver impact (major version bump) and aligns with standard semver terminology
    confidence: 0.95
    alternatives: [schema-breaking, breaking, major-change]
  - id: D-002
    decision: Add autopilot rules, PR+QA gates, and merge validation to ship workflow
    rationale: Release flow was documented but not enforced in the workflow. Zero-HITL rules, branch hierarchy validation, and coreci packaging steps ensure consistent releases
    confidence: 0.90
    alternatives: [keep-as-documentation-only, add-to-AGENTS.md-only]
---/ci---

src/core/ciagent-files.test.ts

@@ -329,7 +329,7 @@ describe("CIAgentFiles", () => {
       expect(ciFiles.getMilestoneType()).toBe("feature");
     });
 
-    it("returns schema-breaking when phases include refactor/rewrite/migrate", () => {
+    it("returns major when phases include refactor/rewrite/migrate", () => {
       const ciFiles = new CIAgentFiles(dir, "schema-proj");
       ciFiles.ensureProjectDir();
       fs.writeFileSync(path.join(dir, ".ciagent", "config.json"), JSON.stringify({
@@ -337,13 +337,13 @@ describe("CIAgentFiles", () => {
         active_project: "schema-proj",
       }));
       const roadmap: RoadmapMd = {
-        overview: "schema-breaking",
+        overview: "major",
         phases: [
           { number: 1, name: "refactor-core", description: "Refactor core", status: "in_progress", dependsOn: [], requirements: [], successCriteria: [] },
         ],
       };
       ciFiles.writeRoadmapMd(roadmap);
-      expect(ciFiles.getMilestoneType()).toBe("schema-breaking");
+      expect(ciFiles.getMilestoneType()).toBe("major");
     });
   });