Revert camera dropdown; add PEER_LINKS for sibling Pis

The dropdown allowed switching the video feed but PTT always pointed at
this Pi's local speaker, so picking a non-co-located camera could have
let a user talk into the wrong room. Each Pi is now hardcoded to the
camera at its own location via CAMERA_NAME, with optional PEER_LINKS to
render quick-jump buttons to sibling doorbell Pis at other URLs.

https://claude.ai/code/session_013XZ1vmgk78k2PEQ5DmJhF3

pi/README.md

@@ -54,22 +54,41 @@ experience.
 
 ## Choosing the camera
 
-`server.py` near the top has the list of cameras the page offers:
+Each Pi is hardcoded to one camera -- the one whose mic and speaker are
+physically co-located with this Pi. The PTT button on this page only
+talks to *this* Pi's speaker, so mixing cameras here would let a misclick
+talk into the wrong room.
+
+`server.py` near the top:
 ```python
-CAMERAS = ["front_door"]
+CAMERA_NAME = "front_door"
 ```
 
-Each name must match a `go2rtc.streams` entry in
+The name must match a `go2rtc.streams` entry in
 `frigate_config/config.yml` and the camera must be `enabled: true` in
-Frigate. With more than one entry the page shows a dropdown above the
-talk button; the choice is remembered per-browser in `localStorage`. The
-first entry is the default for new visitors.
-
-After editing:
+Frigate. After editing:
 ```bash
 sudo systemctl restart doorbell
 ```
 
+## Multiple doorbell Pis
+
+Run one copy of this app per Pi, each on its own subdomain (e.g.
+`frontdoor.yourdomain.com`, `backdoor.yourdomain.com`). Add a Caddy
+block per subdomain pointing at that Pi's LAN IP -- same shape as the
+existing `doorbell.yourdomain.com` block in `../caddy/Caddyfile`.
+
+To render quick-jump buttons to the other Pis at the top of the page,
+fill in `PEER_LINKS` near the top of `server.py`:
+```python
+PEER_LINKS = [
+    {"label": "Back door", "url": "https://backdoor.yourdomain.com"},
+    {"label": "Squirrel",  "url": "https://squirrel.yourdomain.com"},
+]
+```
+Leave it as `[]` (the default) and the row is hidden. Restart with
+`sudo systemctl restart doorbell` after editing.
+
 ## Audio stack
 
 ALSA-only -- no PipeWire/PulseAudio. Lighter on the Pi Zero. If you ever