Add map hover/railroad graphics overrides and fix territory highlight

Extend GraphicsOverrides with a mapOverlay group (territory highlight,
border highlight amount, border highlight thickness) and a railroad
group (train track draw distance), wired through the schema,
applyGraphicsOverrides, and new sliders in the graphics settings modal.

Fix the territory hover highlight: the shader received uHighlightBrighten
but ignored it, applying a hardcoded saturation boost so the setting had
no effect. It now drives a contrast boost (push channels away from
mid-gray), with 0 disabling the effect.

The train track slider is presented as a "draw distance" (inverted
railMinZoom) so higher = tracks stay visible when more zoomed out.

Also move the Graphics settings button to the top of the settings modal.

src/client/render/gl/GraphicsOverrides.ts

@@ -14,6 +14,18 @@ export const GraphicsOverridesSchema = z
         classicIcons: z.boolean(),
       })
       .partial(),
+    mapOverlay: z
+      .object({
+        highlightFillBrighten: z.number(),
+        highlightBrighten: z.number(),
+        highlightThicken: z.number(),
+      })
+      .partial(),
+    railroad: z
+      .object({
+        railMinZoom: z.number(),
+      })
+      .partial(),
   })
   .partial();
 

src/client/render/gl/RenderOverrides.ts

@@ -23,6 +23,21 @@ export function applyGraphicsOverrides(
     settings.structure.iconB = 0;
     settings.structure.iconAlpha = 0.75;
   }
+  if (overrides.mapOverlay?.highlightFillBrighten !== undefined) {
+    settings.mapOverlay.highlightFillBrighten =
+      overrides.mapOverlay.highlightFillBrighten;
+  }
+  if (overrides.mapOverlay?.highlightBrighten !== undefined) {
+    settings.mapOverlay.highlightBrighten =
+      overrides.mapOverlay.highlightBrighten;
+  }
+  if (overrides.mapOverlay?.highlightThicken !== undefined) {
+    settings.mapOverlay.highlightThicken =
+      overrides.mapOverlay.highlightThicken;
+  }
+  if (overrides.railroad?.railMinZoom !== undefined) {
+    settings.railroad.railMinZoom = overrides.railroad.railMinZoom;
+  }
   if (overrides.name?.darkNames !== undefined) {
     const dark = overrides.name.darkNames;
     // Dark: black fill + player-colored outline. Force outline RGB to black

src/client/render/gl/shaders/map-overlay/territory.frag.glsl

@@ -21,7 +21,7 @@ uniform float uStaleNukeVariation;
 uniform float uStaleNukeAlpha;
 uniform vec3 uStaleNukeColor;
 uniform uint uHighlightOwner;      // 0 = no highlight; otherwise smallID of hovered owner
-uniform float uHighlightBrighten;  // mix amount toward white for highlighted tiles
+uniform float uHighlightBrighten;  // hover contrast boost strength; 0 = disabled
 uniform sampler2D uDefenseCoverageTex; // R8 — 1.0 = tile defended by same-owner post
 uniform float uDefenseDarken;      // multiplier applied to fill on defended tiles
 uniform sampler2D uBorderTex;      // RGBA8 — border flags; R > 0.25 = border tile
@@ -104,11 +104,11 @@ void main() {
     }
   }
 
-  // Hover highlight: boost saturation on the hovered player's tiles.
-  // luma = grayscale equivalent; mixing past 1.0 pushes color away from gray.
-  if (uHighlightOwner != 0u && owner == uHighlightOwner) {
-    float luma = dot(color.rgb, vec3(0.299, 0.587, 0.114));
-    color.rgb = clamp(mix(vec3(luma), color.rgb, 1.6), 0.0, 1.0);
+  // Hover highlight: boost contrast on the hovered player's tiles, pushing
+  // channels away from mid-gray. uHighlightBrighten is the strength; 0 disables.
+  if (uHighlightOwner != 0u && owner == uHighlightOwner && uHighlightBrighten > 0.0) {
+    float contrast = 1.0 + uHighlightBrighten;
+    color.rgb = clamp((color.rgb - 0.5) * contrast + 0.5, 0.0, 1.0);
   }
 
   // Defense bonus: darken the fill on interior tiles defended by a same-owner