fix: prevent video stretching in timeline scrubbing preview

- MsePlayer: change default object-fit fallback from fill to contain
  (grid layout keeps fill via --frigate-mse-object-fit:fill CSS variable)
- PreviewPlayer: add object-contain class to video element
- HlsVideoPlayer: add object-contain class to video element

Recordings view and timeline preview now preserve aspect ratio,
while live grid continues to stretch corridor cameras as before.

web/src/components/player/HlsVideoPlayer.tsx

@@ -390,7 +390,7 @@ export default function HlsVideoPlayer({
             )}
           <video
             ref={videoRef}
-            className={`size-full rounded-lg bg-black md:rounded-2xl ${loadedMetadata ? "" : "invisible"} cursor-pointer`}
+            className={`size-full object-contain rounded-lg bg-black md:rounded-2xl ${loadedMetadata ? "" : "invisible"} cursor-pointer`}
             preload="auto"
             autoPlay
             controls={!frigateControls}

web/src/components/player/MsePlayer.tsx

@@ -849,7 +849,7 @@ function MSEPlayer({
       className={className}
       style={{
         objectFit:
-          "var(--frigate-mse-object-fit, fill)" as CSSProperties["objectFit"],
+          "var(--frigate-mse-object-fit, contain)" as CSSProperties["objectFit"],
         transform:
           "var(--frigate-mse-grid-rotation, none)" as CSSProperties["transform"],
         transformOrigin:

web/src/components/player/PreviewPlayer.tsx

@@ -303,7 +303,7 @@ function PreviewVideoPlayer({
       {isVisible && (
         <video
           ref={previewRef}
-          className={`absolute size-full ${currentHourFrame ? "invisible" : "visible"}`}
+          className={`absolute size-full object-contain ${currentHourFrame ? "invisible" : "visible"}`}
           preload="auto"
           autoPlay
           playsInline