feat: implement single binary build and env-based auth

- Unify login page styling with share page
- Add AGENTS.md with build commands and code style guidelines
- Add dev.sh and make.sh for development and production builds
- Implement single binary build with embedded frontend using embed.FS
- Change auth configuration from CLI flag to env variables (USHARE_USERNAME, USHARE_PASSWORD)
- Set default credentials: admin / ushare@123
- Fix static file serving for SPA routes

make.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+
+set -e
+
+echo "=========================================="
+echo "  Building UShare Single Binary"
+echo "=========================================="
+echo ""
+
+# 清理旧的构建产物
+echo "[Cleanup] Removing old build files..."
+rm -rf dist
+rm -f ushare
+rm -rf internal/static/frontend
+
+# 构建前端
+echo ""
+echo "[Frontend] Building..."
+cd frontend
+pnpm run build
+cd ..
+
+# 复制前端构建产物到 internal/static
+echo "[Frontend] Copying dist files..."
+mkdir -p internal/static/frontend
+cp -r frontend/dist internal/static/frontend/
+
+# 构建后端（包含嵌入的前端文件）
+echo ""
+echo "[Backend] Building with embedded frontend..."
+mkdir -p dist
+CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -ldflags '-s -w' -o dist/ushare .
+
+# 清理临时文件
+echo ""
+echo "[Cleanup] Removing temporary files..."
+rm -rf internal/static/frontend
+
+echo ""
+echo "=========================================="
+echo "  Build Complete!"
+echo "  Binary: dist/ushare"
+echo "=========================================="
+echo ""
+echo "Usage:"
+echo "  ./dist/ushare -debug -address 0.0.0.0:9119 -data ./data -auth \"admin:password\""
+echo ""
+echo "  Development: ./dev.sh"
+echo "  Production: ./make.sh && ./dist/ushare ..."