Add nuke fallout color graphics option (#4355)

## What

Adds a **Nuke fallout color** option to the in-game graphics settings
modal (Effects section), letting players recolor the fallout tint left
on territory after a nuke.

![modal](https://github.com/user-attachments/assets/placeholder)

## How

Mirrors the existing **Ocean color** override pattern:

- `GraphicsOverrides.ts` — adds `staleNukeColor` (hex string) to the
`mapOverlay` override schema.
- `RenderOverrides.ts` — `applyGraphicsOverrides` parses the hex and
writes the renderer's `staleNukeR/G/B` 0–1 float channels (`hexToRgb`
yields 0–255, so it divides by 255).
- `GraphicsSettingsModal.ts` — new hex-text + native color-picker row,
default computed from `render-settings.json`.
- `en.json` — `nuke_color_label` / `nuke_color_desc`.

The value persists via `UserSettings.graphicsOverrides()` and is cleared
by the modal's existing "Reset to defaults".

The render debug GUI already exposes the same setting as **Stale Nuke
Color** (Map Overlay), so no change was needed there.

## Testing

- `tsc --noEmit` clean.
- Verified in a headless solo game: the row renders with the green
default (`#0d8c12`), changing it persists `mapOverlay.staleNukeColor`,
and `applyGraphicsOverrides("#ff0000")` produces `staleNukeR=1, G=0,
B=0`.

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

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

resources/lang/en.json

@@ -547,6 +547,8 @@
     "name_cull_desc": "Hide names smaller than this size",
     "name_cull_label": "Minimum name size",
     "name_scale_label": "Name Scale",
+    "nuke_color_desc": "Color of the fallout tint left on territory after a nuke.",
+    "nuke_color_label": "Nuke fallout color",
     "ocean_color_desc": "Base color of ocean.",
     "ocean_color_label": "Ocean color",
     "rail_distance_desc": "How far zoomed out train tracks remain visible",