feat: friends panel (#3990)

## Description:

# Add Friends tab to Account modal

## Summary

- Adds a "Friends" tab to the Account modal, alongside Account / Stats /
Games.
- New `<friends-list>` Lit component covering the full friend lifecycle:
send request, accept / deny incoming, withdraw outgoing, remove friend,
paginated list with "Load more".
- New `FriendsApi.ts` wrapping `GET/POST/DELETE /friends*` endpoints
with typed error codes (`not_found` / `conflict` / `bad_request` /
`request_failed`).
- Zod schemas for the friend API responses in `core/ApiSchemas.ts`.
- Translations under a new `friends.*` block in `en.json`.

Friends and pending requests are displayed by public ID via
`copy-button`, matching the existing clan convention.


## 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/core/ApiSchemas.ts

@@ -218,6 +218,35 @@ export type RankedLeaderboardResponse = z.infer<
   typeof RankedLeaderboardResponseSchema
 >;
 
+export const FriendEntrySchema = z.object({
+  publicId: z.string(),
+  createdAt: z.iso.datetime(),
+});
+export type FriendEntry = z.infer<typeof FriendEntrySchema>;
+
+export const FriendRequestsResponseSchema = z.object({
+  incoming: FriendEntrySchema.array(),
+  outgoing: FriendEntrySchema.array(),
+});
+export type FriendRequestsResponse = z.infer<
+  typeof FriendRequestsResponseSchema
+>;
+
+export const FriendsListResponseSchema = z.object({
+  results: FriendEntrySchema.array(),
+  total: z.number(),
+  page: z.number(),
+  limit: z.number(),
+});
+export type FriendsListResponse = z.infer<typeof FriendsListResponseSchema>;
+
+export const SendFriendRequestResponseSchema = z.object({
+  status: z.enum(["requested", "accepted"]),
+});
+export type SendFriendRequestResponse = z.infer<
+  typeof SendFriendRequestResponseSchema
+>;
+
 export const NewsItemSchema = z.object({
   id: z.string(),
   title: z.string(),