Move theme data into the render-settings JSON pipeline (#4223)

**Add approved & assigned issue number here:**

N/A — maintainer refactor.

## Description:

Replaces the theme class hierarchy
(`BaseTheme`/`PastelTheme`/`ColorblindTheme`) with theme JSON files —
`default-theme.json` and `colorblind-theme.json` — combined with
`render-settings.json` at runtime into a single graphics-configuration
pipeline (`settings.theme`). One `SettingsTheme` class keeps the
algorithms (color allocation, team-variation generation, LAB-contrast
structure colors) and reads all data from `ThemeSettings`; adding a
theme is now just adding a JSON file.

Colorblind mode (#4150) is fully preserved:

- Same palettes — the 32-color CVD-safe pool and Okabe-Ito team colors
are baked into `colorblind-theme.json`
- The relative border rule (`l × 0.6`) is expressed as a
`borderLightnessScale` knob alongside the default theme's absolute
`borderDarken`
- The mid-game re-theme wiring (`refreshPlayerColors`/`refreshPalette`)
and the affiliation/friend-foe tint overrides are unchanged;
`applyGraphicsOverrides` now also swaps the `settings.theme` slice
- `deepAssign` replaces arrays wholesale so differing palette lengths
survive theme switches

Verified against the previous implementation with an equivalence test
(since removed): default-theme colors are byte-identical including
allocation order; colorblind team/derived colors are byte-identical, and
FFA assignment may permute within the same palette (hex baking rounds
upstream's fractional-RGB colord objects, which can flip the allocator's
greedy delta-E ordering — rendered colors round identically either way).

Also removes dead theme surface (`terrainColor`, `backgroundColor`,
`falloutColor`, `font`, `textColor`, spawn-highlight variants,
`PastelThemeDark`) — GL terrain colors and dark mode were already
handled in the renderer. Note this means the colorblind terrain bands
from #4150 were dead code (nothing calls `terrainColor`; GL terrain
comes from `ColorUtils.encodeTerrainTile`); wiring CVD-safe terrain into
the terrain texture would be a follow-up.

## Please complete the following:

- [x] I have added screenshots for all UI updates — N/A, no UI changes
(verified color-identical)
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file — N/A, no user-visible text
- [x] I have added relevant tests to the test directory —
`tests/Colors.test.ts` updated for the new pipeline (team colors from
theme JSON, colorblind palette/border tests)

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evanpelle

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

tests/util/viewStubs.ts

@@ -7,7 +7,7 @@
  */
 
 import { colord } from "colord";
-import { Theme } from "../../src/client/theme/Theme";
+import { Theme } from "../../src/client/theme/ThemeProvider";
 import { GameView } from "../../src/client/view/GameView";
 import { PlayerView } from "../../src/client/view/PlayerView";
 import { Config } from "../../src/core/configuration/Config";
@@ -40,15 +40,7 @@ export function stubTheme(): Theme {
     borderColor: () => grey,
     defendedBorderColors: () => defended,
     focusedBorderColor: () => grey,
-    terrainColor: () => white,
-    backgroundColor: () => white,
-    falloutColor: () => white,
-    font: () => "Arial",
-    textColor: () => "#000000",
     spawnHighlightColor: () => white,
-    spawnHighlightSelfColor: () => white,
-    spawnHighlightTeamColor: () => white,
-    spawnHighlightEnemyColor: () => white,
   };
 }