feat(highlight): replace the small-player highlight toggle with a strength slider (#4588)

## Description:

Replaces the "Highlight small players" on/off toggle with a **0-500%
Strength slider** controlling the glow's **width** (0 = off, 100% = the
previous default).

- `UserSettings`: `highlightSmallPlayers()`/toggle →
`highlightGlowStrength()`/set, float-backed, clamped to [0, 5].
- `SmallPlayerGlowPass` takes the strength via a setter (pushed by
`ClientGameRunner` on the settings-changed event), so it stays a pure
consumer and the slider still updates live while the settings modal has
the sim paused. Width = a non-linear blur-iteration count; intensity
compensated so wider stays about as bright.
- `MapRenderer` persists the strength across a WebGL context restore.
- `SettingsModal`: the toggle row becomes a range input.

Behavior note: with the toggle gone the glow **defaults ON at 100%**
(old toggle defaulted OFF); can default to 0 (opt-in) if preferred.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory

src/core/game/UserSettings.ts

@@ -139,8 +139,11 @@ export class UserSettings {
     return this.getBool("settings.emojis", true);
   }
 
-  highlightSmallPlayers() {
-    return this.getBool("settings.highlightSmallPlayers", false);
+  highlightGlowStrength() {
+    // 0 = off, 1 = default; capped at 5 (the 500% slider max) so a value
+    // persisted from an older, larger range can't display/apply above it.
+    const v = this.getFloat("settings.highlightGlowStrength", 1);
+    return Math.min(5, Math.max(0, v));
   }
 
   performanceOverlay() {
@@ -195,11 +198,8 @@ export class UserSettings {
     this.setBool("settings.emojis", !this.emojis());
   }
 
-  toggleHighlightSmallPlayers() {
-    this.setBool(
-      "settings.highlightSmallPlayers",
-      !this.highlightSmallPlayers(),
-    );
+  setHighlightGlowStrength(value: number) {
+    this.setFloat("settings.highlightGlowStrength", value);
   }
 
   // Performance overlay specifically needs a direct setter for Shift-D