docs: clarify NetBird built-in SSH vs regular SSH

Dashboard's 'SSH Access is disabled' warning confuses new users
who can clearly ssh into peers just fine. These are two different
systems: Dashboard's SSH Access is NetBird's own in-daemon SSH
tunnel server (accessed via Dashboard Connect button or
'netbird ssh'), while the regular ssh command uses the target
machine's OpenSSH running on port 22 and has nothing to do with
the Dashboard SSH toggle.

Home-lab use cases rarely need the NetBird built-in SSH — regular
OpenSSH over the NetBird overlay is sufficient. Doc explains when
you would actually want it (browser-based terminal from Dashboard,
credential offloading to NetBird identity, etc) and how to enable
if needed.

SUMMARY.md

@@ -90,6 +90,7 @@ reopen fd 8: permission denied
 | 新 peer `netbird status` 顯示 Connected 但互 ping 都不通 | 主機同時跑 Tailscale kernel-mode，`iptables-legacy ts-input` 把 `100.64.0.0/10` 非 tailscale0 封包全 drop，NetBird `100.71.0.0/16` 中彈 | `iptables-legacy -I INPUT 1 -i wt0 -j ACCEPT` + FORWARD 同理；systemd 持久化；詳見 [peer-deployment-ops.md](./peer-deployment-ops.md) |
 | 加 subnet route 後部分裝置拿不到路由（`Networks: -`、`Status: Connecting`） | 既有 NetBird daemon 不會自動重新套用 route，卡在舊 state | 各裝置重連 daemon：macOS `launchctl kickstart`、iOS App Disconnect→Connect、Docker `compose restart`；見 [network-routes.md](./network-routes.md) |
 | iPhone RTSP app 連不到 LAN 攝影機（Safari 打 HTTP 可以） | 某些 iOS app 不走系統 VPN 路由 | 換支援 VPN 的 app（VLC 等），或改用 NetBird FQDN |
+| Dashboard 顯示 "SSH Access is disabled" 但 `ssh` 指令照通 | Dashboard 的 "SSH Access" 是 NetBird 內建 SSH 通道，不等於目標機器的 OpenSSH | 兩種 SSH 是不同東西，不用理會那個提示；見 [ssh-access.md](./ssh-access.md) |
 
 ## 檔案位置
 
@@ -106,7 +107,8 @@ reopen fd 8: permission denied
 ├── client-troubleshooting.md         ← 客戶端 Force Relay / bufferbloat 排錯
 ├── peer-deployment-ops.md            ← Docker 部署客戶端、改名、Mac daemon 重啟
 ├── groups-and-policies.md            ← Groups 與 Access Control 設計與操作
-└── network-routes.md                 ← Subnet Router 讓 peer 存取 LAN 非 NetBird 裝置
+├── network-routes.md                 ← Subnet Router 讓 peer 存取 LAN 非 NetBird 裝置
+└── ssh-access.md                     ← 一般 SSH vs NetBird 內建 SSH 的差別
 ```
 
 ### 遠端伺服器（192.168.42.127:/opt/netbird/）