ci: add upstream sync workflows and optimize Docker CI builds

- Add auto-upstream-sync workflow with dedup protection for conflict issues
- Add upstream-sync build + smoke test workflow
- Add smoke-test script and test files
- Add upstream sync issue template and documentation
- Fix: use --allow-unrelated-histories for merge command
- Fix: check for existing open merge-conflict issues before creating duplicates

.github/ISSUE_TEMPLATE/upstream-sync.md

@@ -0,0 +1,33 @@
+---
+name: Upstream Sync Report
+about: Auto-generated report for upstream sync
+title: '🔄 Upstream Sync: {{ date | date("YYYY-MM-DD") }}'
+labels: upstream-sync, automated
+assignees: ""
+---
+
+## 🔄 Upstream 自動同步報告
+
+**同步日期:** {{ date }}
+**新 Commits:** {{ commit_count }}
+
+### 📝 變更摘要
+
+```
+{{ commits_list }}
+```
+
+### 🐳 Docker Image
+
+- **Tag:** `upstream-{{ date_tag }}`
+- **Smoke Test:** {{ smoke_test_status }}
+
+### ⏳ 後續動作
+
+- [ ] 檢視變更內容
+- [ ] 確認 smoke test 結果
+- [ ] 決定是否 merge 到 main
+
+---
+
+_此 Issue 由 GitHub Actions 自動建立_