Add NSCalibratedRGBColorSpace support.

**Problems**

Ghostty is using sRGB by default, optionally Display P3 color space.
However neither color space matches to the color space that the regular
macOS apps are using.
That is `NSCalibratedRGBColorSpace`, seems called "Generic RGB" from
initializer API name.

Because of this, colors has same hex value are slightly darker on
Ghostty compare to Terminal.app, for example.

**Solution**

Add `generic-rgb` to `WindowColorspace`, therefore users can set
`window-colorspace` to `generic-rgb` in config to have similar colors
with the other macOS apps.

macos/Sources/Features/QuickTerminal/QuickTerminalController.swift

@@ -322,6 +322,8 @@ class QuickTerminalController: BaseTerminalController {
         switch (self.derivedConfig.windowColorspace) {
         case "display-p3":
             window.colorSpace = .displayP3
+        case "generic-rgb":
+            window.colorSpace = .genericRGB
         case "srgb":
             fallthrough
         default:

macos/Sources/Features/Terminal/TerminalController.swift

@@ -301,6 +301,8 @@ class TerminalController: BaseTerminalController {
         switch (config.windowColorspace) {
         case "display-p3":
             window.colorSpace = .displayP3
+        case "generic-rgb":
+            window.colorSpace = .genericRGB
         case "srgb":
             fallthrough
         default:

src/config/Config.zig

@@ -5291,6 +5291,7 @@ pub const WindowTheme = enum {
 pub const WindowColorspace = enum {
     srgb,
     @"display-p3",
+    @"generic-rgb",
 };
 
 /// See macos-titlebar-style