feat(plex): subtitles rise above the control bar while it shows

On an iPad the bar covered the text whenever it was up: the browser places a
native cue by its line, which nothing animates. The track now stays loaded as
hidden and PlexSubtitles draws the active cues, measured against the bar and
lifted above it in 200 ms, back down when it hides. The viewer's size, colour,
background and outline settings style the text directly. Also fixes a test
typing slip from the search pill change.

frontend/src/lib/plexPlayerPrefs.ts

@@ -78,9 +78,9 @@ export const DEFAULT_PREFS: PlexPlayerPrefs = {
 // A punchy subtitle shadow. The old single 0-offset blur washed out to nothing on bright scenes even
 // at the max slider value; instead lay down eight offset copies (a solid dark OUTLINE around the
 // glyphs) plus a soft glow, all scaled by the slider — legible over anything, e.g. yellow text on a
-// snow-white frame. Empty string when the slider is 0 (shadow off).
-export function subShadowCss(px: number, color: string): string {
-  if (px <= 0) return "";
+// snow-white frame. A `text-shadow` value; undefined when the slider is 0 (shadow off).
+export function subShadow(px: number, color: string): string | undefined {
+  if (px <= 0) return undefined;
   const o = px;
   const b = Math.max(1, Math.round(px / 2));
   const dirs: [number, number][] = [
@@ -94,7 +94,7 @@ export function subShadowCss(px: number, color: string): string {
     [-o, -o],
   ];
   const outline = dirs.map(([x, y]) => `${x}px ${y}px ${b}px ${color}`).join(",");
-  return `text-shadow:${outline},0 0 ${o * 2}px ${color};`;
+  return `${outline},0 0 ${o * 2}px ${color}`;
 }
 
 // Top-right wall clock text: time (24h European or 12h am/pm) + optional date in one of two fixed