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

resources/lang/en.json

@@ -656,7 +656,8 @@
     "choose_spawn": "Choose a starting location"
   },
   "territory_patterns": {
-    "title": "Select Territory Skin",
+    "title": "Skins",
+    "colors": "Colors",
     "purchase": "Purchase",
     "blocked": {
       "login": "You must be logged in to access this pattern.",