fix: possibility for negative values in gold and troop donation (#2810)

## Description:

Previously, the zod schemas for troop and gold donation allowed for
negative values which could open the game up to vulnerabilities through
undefined behavior in the future. We mitigate these vulnerabilities but
adding `.nonnegative` to the `DonateGoldIntentSchema` and
`DonateTroopIntentShcema` respectively. Today, code exists to prevent
this deeper in the codebase, but we should also prevent this earlier if
possible during intent validation.

## 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:

haticus

src/core/Schemas.ts

@@ -309,13 +309,13 @@ export const EmbargoAllIntentSchema = BaseIntentSchema.extend({
 export const DonateGoldIntentSchema = BaseIntentSchema.extend({
   type: z.literal("donate_gold"),
   recipient: ID,
-  gold: z.number().nullable(),
+  gold: z.number().nonnegative().nullable(),
 });
 
 export const DonateTroopIntentSchema = BaseIntentSchema.extend({
   type: z.literal("donate_troops"),
   recipient: ID,
-  troops: z.number().nullable(),
+  troops: z.number().nonnegative().nullable(),
 });
 
 export const BuildUnitIntentSchema = BaseIntentSchema.extend({