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)

.gitignore

@@ -3,4 +3,11 @@ test/
 demo/
 *.log
 *.db
-.env
+.env
+
+# 构建产物（make web 生成，由 go:embed 打进二进制）；保留 .gitkeep 占位使未构建前也能编译
+cmd/openteam/dist/*
+!cmd/openteam/dist/.gitkeep
+
+# 误生成的目录（仅含 dist/node_modules）
+web/