feat: make session creation a sequential workflow

- Refactor CreateSessionForm into step-by-step workflow
- Steps unlock sequentially: Project → Repository → Tool → Clone Mode → Branch
- Add visual step indicators with numbered badges
- Disable controls until prerequisites are met
- Add CSS for workflow step styling

.stoneforge/sync/dependencies.jsonl

@@ -0,0 +1 @@
+{"blockedId":"el-1of","blockerId":"el-258","type":"parent-child","createdAt":"2026-05-24T09:44:58.759Z","createdBy":"el-2jua"}