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

tests/UserSettings.test.ts

@@ -59,7 +59,7 @@ describe("UserSettings effect selection", () => {
   });
 });
 
-describe("UserSettings highlight small players", () => {
+describe("UserSettings highlight glow strength", () => {
   beforeEach(() => {
     localStorage.clear();
     (
@@ -67,22 +67,22 @@ describe("UserSettings highlight small players", () => {
     ).cache.clear();
   });
 
-  it("defaults to off", () => {
-    expect(new UserSettings().highlightSmallPlayers()).toBe(false);
+  it("defaults to 1 (100%, on)", () => {
+    expect(new UserSettings().highlightGlowStrength()).toBe(1);
   });
 
-  it("toggles on and off", () => {
+  it("persists a set value, including 0 (off)", () => {
     const s = new UserSettings();
-    s.toggleHighlightSmallPlayers();
-    expect(s.highlightSmallPlayers()).toBe(true);
-    s.toggleHighlightSmallPlayers();
-    expect(s.highlightSmallPlayers()).toBe(false);
+    s.setHighlightGlowStrength(2.5);
+    expect(s.highlightGlowStrength()).toBe(2.5);
+    s.setHighlightGlowStrength(0);
+    expect(s.highlightGlowStrength()).toBe(0);
   });
 
   it("shares state across instances via the static cache", () => {
     // The settings modal and the renderer's frame builder each hold their own
-    // UserSettings; a toggle in one must be visible to the other.
-    new UserSettings().toggleHighlightSmallPlayers();
-    expect(new UserSettings().highlightSmallPlayers()).toBe(true);
+    // UserSettings; a change in one must be visible to the other.
+    new UserSettings().setHighlightGlowStrength(3);
+    expect(new UserSettings().highlightGlowStrength()).toBe(3);
   });
 });