TypeScript update to 6.0.3 (#3806)

## Description:

Updating TypeScript to 6.0.3.
Updating TypeScript-eslint to 8.59.1 for TS6 support.
Concurrently needed to get updated as well to remove deprecated warning.

Most things deleted are now just defaults.

## 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:

Babyboucher

src/server/Privilege.ts

@@ -176,21 +176,24 @@ export class PrivilegeCheckerImpl implements PrivilegeChecker {
           refs.patternColorPaletteName ?? null,
         );
       } catch (e) {
-        return { type: "forbidden", reason: "invalid pattern: " + e.message };
+        const message = e instanceof Error ? e.message : String(e);
+        return { type: "forbidden", reason: "invalid pattern: " + message };
       }
     }
     if (refs.color) {
       try {
         cosmetics.color = this.isColorAllowed(flares, refs.color);
       } catch (e) {
-        return { type: "forbidden", reason: "invalid color: " + e.message };
+        const message = e instanceof Error ? e.message : String(e);
+        return { type: "forbidden", reason: "invalid color: " + message };
       }
     }
     if (refs.flag) {
       try {
         cosmetics.flag = this.isFlagAllowed(flares, refs.flag);
       } catch (e) {
-        return { type: "forbidden", reason: "invalid flag: " + e.message };
+        const message = e instanceof Error ? e.message : String(e);
+        return { type: "forbidden", reason: "invalid flag: " + message };
       }
     }