feat(P06): 3-tier versioning, branch hierarchy enforcement, ARCHITECTURE-PLAN synthesis

---ci---
phase: 6
milestone: v0.5
status: complete
decisions:
  - id: D-006
    decision: Research as intermediate work product
    rationale: Conclusions update .ci/ files; full research doc intentionally not preserved
    confidence: 0.90
  - id: D-007
    decision: Branch hierarchy enforcement: main > milestone > phase
    rationale: Prevents out-of-order merges and semantically wrong tags
    confidence: 0.92
  - id: D-008
    decision: 3-tier versioning: NFR/feature/schema-breaking
    rationale: Patch per phase (NFR/feature) or minor per phase (schema-breaking); milestone gets minor (feature) or major (schema-breaking)
    confidence: 0.95
requirements:
  covered: [VER-06, BRANCH-01, BRANCH-02, ARCH-01]
---/ci---

- Synthesize ARCHITECTURE-PLAN.md into .ci/ci/ARCHITECTURE.md (expanded 51→230 lines)
- Add D-006/D-007/D-008 to .ci/ci/PROJECT.md key decisions table
- Delete ARCHITECTURE-PLAN.md after synthesis
- Rewrite ship.md with 3-tier versioning model + branch hierarchy merge flows
- Rewrite branch-strategy.md with 3-tier versioning + branch hierarchy + version validation
- Add MilestoneType to config types
- Replace isNfrMilestone() with getMilestoneType() returning nfr|feature|schema-breaking
- Add validateMergeOrder(), mergeMilestoneBranch(), computeMilestoneTag() to GitBranch
- Add computeShipVersion(), validateVersionOrder(), resolveMergeTarget() to ship command
- Remove hardcoded v0.5. from error-recovery rollback
- Create .githooks/pre-push for semver ordering + branch hierarchy validation
- Add 15 new tests (370 total, all passing)

src/core/git-context.test.ts

@@ -279,4 +279,45 @@ status: execute
       expect(ctx.isNfrMilestone()).toBe(false);
     });
   });
+
+  describe("getMilestoneType", () => {
+    it("returns nfr when only NFR commits exist", () => {
+      commit(repoDir, `chore(P01): cleanup
+
+---ci---
+phase: 1
+milestone: v0.1.1
+status: execute
+---/ci---`);
+
+      const ctx = new GitContext(repoDir);
+      expect(ctx.getMilestoneType()).toBe("nfr");
+    });
+
+    it("returns feature when feat commits exist", () => {
+      commit(repoDir, `feat(P01): add feature
+
+---ci---
+phase: 1
+milestone: v1.0
+status: execute
+---/ci---`);
+
+      const ctx = new GitContext(repoDir);
+      expect(ctx.getMilestoneType()).toBe("feature");
+    });
+
+    it("returns schema-breaking when refactor commits exist", () => {
+      commit(repoDir, `refactor(P01): rewrite core
+
+---ci---
+phase: 1
+milestone: v0.5
+status: execute
+---/ci---`);
+
+      const ctx = new GitContext(repoDir);
+      expect(ctx.getMilestoneType()).toBe("schema-breaking");
+    });
+  });
 });