feat: HomeDash - unified self-hosted navigation portal

Single-container navigation service combining:
- Dashy dashboard + SearXNG metasearch + history sync API + admin WebUI
- Go services for history/admin APIs, nginx as unified entry
- Browser extensions (Chrome MV3 / Firefox MV2) with 30s batched sync
- Production guide: portal-nginx unified auth reverse proxy + webui4frpc/frp tunnel
- Fully sanitized (no internal IPs/domains/credentials)

.env.example

@@ -0,0 +1,8 @@
+# JianF 统一导航服务环境变量
+# 复制此文件为 .env 并修改
+
+# 浏览器插件同步令牌（留空则不鉴权）
+NAVI_SYNC_TOKEN=
+
+# 管理 API 令牌（留空则不鉴权）
+NAVI_ADMIN_TOKEN=