Live view improvements (#24967)

* hold the last frame on screen while switching live streams

Switching streams in the single camera view blanked the player until the new stream played, because the old player unmounts in the same render and the hidden new player gave the card no height. The outgoing video's last frame is now drawn to a canvas before the remount and covers the gap until the new stream plays, and the card takes the camera's aspect ratio so it keeps its size while the video is hidden.

* show live streams as a one-tap grid in the mobile drawer

Switching streams on mobile meant scrolling past the camera toggles, opening a dropdown, and picking a stream. The drawer now opens with the stream section, and streams are a wrapping grid of toggles sized to their names, so a switch is two taps. A single stream shows as plain text. The audio and two-way talk lines show a spinner while the stream's go2rtc metadata loads instead of reporting audio as unavailable, which showed on the first switch to a transcoded stream.

* don't capture the switch frame on tiles that show the camera still

web/public/locales/en/views/live.json

@@ -173,6 +173,9 @@
       "label": "Play in background",
       "tips": "Enable this option to continue streaming when the player is hidden."
     },
+    "metadata": {
+      "loading": "Fetching stream metadata…"
+    },
     "mode": "Streaming Technology",
     "technology": {
       "description": "Choose your preferred streaming technology. Frigate may still fall back to low bandwidth mode on playback or network errors.",