Add ocean color override to graphics settings (#4269)

## What

Adds a **Terrain** section to the graphics settings modal with a color
picker and a hex-code text field (paste a `#rrggbb` code) for the
**ocean** (deep water) color.

## Details

- The picked color sets the *shallow-water base*; the existing per-depth
brightness gradient is preserved (deeper water still darkens).
- Only deep water is affected — shoreline water and land are untouched.
- Follows the same override pattern as every other graphics setting: the
default lives in `render-settings.json` (`terrain.oceanColor`), the
override is a field in `GraphicsOverrides`, and `applyGraphicsOverrides`
copies it into the live `RenderSettings`.
- Rebased on #4271 (settings resolved before renderer construction): the
terrain texture **bakes the resolved ocean color at construction**, so a
saved override shows on load with no special-casing. Terrain is baked
into a GPU texture rather than read per-frame, so a *live* change still
triggers an explicit `view.rebuildTerrain()`.
- Resetting graphics overrides clears it back to the default ocean
color.

## Testing
Verified live in a headless singleplayer game:
- A **saved** ocean override renders green deep-water on load, baked at
construction with no settings-change event fired.
- A mid-game color change recolors the deep ocean instantly, gradient
preserved, shoreline/land untouched.

`tsc` and ESLint clean.

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

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

src/client/ClientGameRunner.ts

@@ -521,14 +521,18 @@ async function createClientGame(
     // graphics-override change (covers a theme switch such as colorblind mode).
     const onGraphicsChanged = (): void => {
       regenerateRenderSettings();
+      // Terrain is baked into a GPU texture rather than read per-frame, so a
+      // terrain-color override (e.g. ocean) needs an explicit texture rebuild.
+      view.rebuildTerrain();
       // A graphics override can switch the active theme (e.g. colorblind mode),
       // so re-theme existing players and re-upload the palette to recolor their
       // territory fills/borders live.
       gameView.refreshPlayerColors();
       webglBuilder.refreshPalette(gameView);
     };
-    // No initial regenerate needed — the renderer was constructed with the
-    // resolved settings above.
+    // No initial regenerate or terrain rebuild needed — the renderer was
+    // constructed with the resolved settings above, so the terrain texture
+    // already bakes any saved ocean-color override.
     globalThis.addEventListener(
       `${USER_SETTINGS_CHANGED_EVENT}:${GRAPHICS_KEY}`,
       onGraphicsChanged,