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/git-context.test.ts

@@ -307,7 +307,7 @@ status: execute
       expect(ctx.getMilestoneType()).toBe("feature");
     });
 
-    it("returns schema-breaking when refactor commits exist", () => {
+    it("returns major when refactor commits exist", () => {
       commit(repoDir, `refactor(P01): rewrite core
 
 ---ci---
@@ -317,7 +317,7 @@ status: execute
 ---/ci---`);
 
       const ctx = new GitContext(repoDir);
-      expect(ctx.getMilestoneType()).toBe("schema-breaking");
+      expect(ctx.getMilestoneType()).toBe("major");
     });
   });
 });