refactor: frontend TS migration + Tailwind4/daisyUI5 unify + BUILDPLATFORM docker build

- migrate frontend to TypeScript (vue-tsc strict in build), upgrade all deps to latest (Vite 8, Tailwind 4, daisyUI 5, Pinia 4, vue-router 5)
- restructure frontend dirs (api/components/common/layouts/styles/types/views)
- drop Element Plus, add daisyUI TagInput; main CSS 490KB->163KB, entry JS 618KB->1.3KB
- rewrite Dockerfile(.cn): frontend/backend stages pinned to $BUILDPLATFORM, CGO_ENABLED=0 cross-compile, no QEMU in multi-arch builds; add .dockerignore
- local dev: Vite /api proxy + make dev targets; go:embed all:dist with .gitkeep so backend runs without prior frontend build
- fix latent bugs: Keys.vue users ref, Settings.vue undefined userStore, Login.vue Ref-as-error display, res.error misuse
- add REFACTOR_PLAN.md (phased refactor log)

.dockerignore

@@ -0,0 +1,21 @@
+# 版本管理
+.git
+.gitignore
+
+# 前端依赖与本地构建产物（镜像内由 pnpm 重新安装、重新构建）
+**/node_modules
+frontend/dist
+web
+
+# Go 构建产物
+bin
+cmd/openteam/dist
+
+# 文档与 CI
+doc
+.envci.yaml
+tag.yaml
+
+# 日志与数据库
+*.log
+*.db