Devices: several headsets, several addresses each, and live connection status

Frame Control can now manage more than one Steam Frame, and reach each at any
of several addresses (LAN IPs per network, its .local name, Tailscale). A
connector in the server tries them all at once, picks the best one that
answers, follows ssh -v through each stage (network, finding, SSH, identity,
login) and streams that to the page. The header shows it live; a new Devices
tab (key 5) manages headsets, addresses and network names.

- ui/frame_devices.py: registry in devices.json, imported from the managed
  ~/.ssh/config blocks; per-headset host key pinning; config block updates.
- ui/frame_network.py: gateway IP+MAC fingerprint, Wi-Fi name, Tailscale.
- ui/frame_link.py: the connector, Test now, Tailscale/mDNS discovery, API.
- server.py: ensure_master delegates to the connector; /api/connection,
  /api/connection/events (SSE), /api/devices.
- Electron: headset switcher and Devices item in the Frame menu.
- frame_connect.py --alias; FRAME_CONTROL_DATA_DIR / FRAME_CONTROL_SSH_DIR
  keep tests off real data.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

app/preload.js

@@ -2,7 +2,8 @@
 // to the Frame needs no pbpaste, PowerShell, xclip or wl-clipboard. Also tells
 // the page where a dropped file or folder lives, so a folder can be sideloaded
 // as a title without zipping it (the local server reads it from there).
-// It can open Set Up Connection when the headset can't be reached.
+// It can open Set Up Connection when the headset can't be reached, and keeps the
+// Frame menu's list of headsets up to date.
 // It also receives frame-control://install links (docs/web-install.md): only
 // what the link asked for, never an install; the page asks the user first.
 const { contextBridge, ipcRenderer, webUtils } = require("electron");
@@ -10,6 +11,12 @@ const { contextBridge, ipcRenderer, webUtils } = require("electron");
 contextBridge.exposeInMainWorld("frameApp", {
   readClipboard: () => ipcRenderer.invoke("clipboard:read"),
   setUpConnection: () => ipcRenderer.invoke("connection:setup"),
+  // The Frame menu's headset switcher: the page tells it the headsets, and hears picks.
+  devicesChanged: (list) => ipcRenderer.send("devices:changed", list),
+  onUseDevice: (cb) => {
+    ipcRenderer.removeAllListeners("use-device");
+    ipcRenderer.on("use-device", (_e, id) => cb(String(id)));
+  },
   pathForFile: (file) => { try { return webUtils.getPathForFile(file) || ""; } catch { return ""; } },
   onInstallLink: (cb) => {
     ipcRenderer.removeAllListeners("install-link");