Add territory saturation and opacity graphics settings

Expose two new user-configurable map-overlay controls in the graphics
settings modal: territory saturation (mutes fill colors toward grayscale)
and territory opacity (lets terrain show through the fill).

The territory fragment shader blends the fill toward its luminance based
on uSaturation and applies uTerritoryAlpha as the absolute fill opacity.
Both are wired through RenderSettings, the GraphicsOverrides schema,
applyGraphicsOverrides, the debug Layout sliders, and TerritoryPass
uniforms, with defaults (saturation 1, alpha 0.588) in render-settings.json.
Adds the corresponding en.json label/description strings.

resources/lang/en.json

@@ -945,6 +945,10 @@
     "highlight_brighten_desc": "How strongly the border brightens on hover (0 to disable)",
     "highlight_thicken_label": "Border highlight thickness",
     "highlight_thicken_desc": "How much the border thickens on hover",
+    "territory_sat_label": "Territory saturation",
+    "territory_sat_desc": "How vivid the territory fill colors are (lower mutes them)",
+    "territory_alpha_label": "Territory opacity",
+    "territory_alpha_desc": "How opaque the territory fill is (lower lets terrain show through)",
     "rail_distance_label": "Train track draw distance",
     "rail_distance_desc": "How far zoomed out train tracks remain visible",
     "section_effects": "Effects",