fix(cd): runs-on 改回 ubuntu-latest (Gitea runner label 不支援 self-hosted)

根因: Gitea act_runner 只有 ubuntu-latest/24.04/22.04 labels
     改為 self-hosted 後 runner 無法匹配 → CD 靜默失敗
     所有 Phase 24 代碼都沒部署到 K8s

Gitea ≠ GitHub: GitHub 有內建 self-hosted label
                Gitea 需要明確匹配 runner 註冊的 label

2026-04-02 ogt: CD 失敗根因修復

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/cd.yaml

@@ -30,8 +30,9 @@ env:
 
 jobs:
   build-and-deploy:
-    # 2026-04-02 Claude Code: 修正為 self-hosted (ADR-039 鐵律 + feedback_github_billing.md)
-    runs-on: self-hosted
+    # 2026-04-02 ogt: Gitea runner label 是 ubuntu-latest (非 GitHub 的 self-hosted)
+    # ADR-039 鐵律: 使用自建 runner，但 Gitea label matching 不同於 GitHub
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4