chore(mining-admin-web): 添加.gitignore文件

忽略以下自动生成的文件:
- node_modules/
- .next/
- next-env.d.ts
- *.tsbuildinfo
- .env*.local

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mining-admin-web/.gitignore

@@ -0,0 +1,49 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+.yarn/install-state.gz
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# local env files
+.env*.local
+.env.local
+
+# Claude Code
+.claude/
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# OS
+Thumbs.db