add support for custom colors (#2103)

## Description:

Added a colors tab in territory patterns modal so players can select
their color.

Refactored the PrivilegeChecker, removed custom flag checks since we no
longer support custom flags.

<img width="479" height="345" alt="Screenshot 2025-09-27 at 5 01 17 PM"
src="https://github.com/user-attachments/assets/ad96da65-f0eb-4731-a861-e6e5fcb4566a"
/>
## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

src/client/SinglePlayerModal.ts

@@ -449,6 +449,8 @@ export class SinglePlayerModal extends LitElement {
       ? (this.userSettings.getDevOnlyPattern() ?? null)
       : null;
 
+    const selectedColor = this.userSettings.getSelectedColor();
+
     this.dispatchEvent(
       new CustomEvent("join-lobby", {
         detail: {
@@ -466,6 +468,7 @@ export class SinglePlayerModal extends LitElement {
                       ? ""
                       : flagInput.getCurrentFlag(),
                   pattern: selectedPattern ?? undefined,
+                  color: selectedColor ? { color: selectedColor } : undefined,
                 },
               },
             ],