fix(avatars): every signed-in account sees other users' pictures

System Health shows every user's name and avatarAt to everyone, but the
picture route GET /api/users/:id/avatar sat under the staff-only /users
prefix, so a developer got 403 EADMIN and saw only initials. authGuard now
lets any signed-in account make that one read (EVERYONE_READS); every
other /users path stays staff-only, and the test checks both.

client/src/components/users/UserAvatar.tsx

@@ -2,7 +2,7 @@
  * @file UserAvatar.tsx
  * @description An account's round picture: the signed-in account's own
  * (`GET /api/me/avatar`) or, with `userId`, another's (`GET
- * /api/users/:id/avatar`, staff only), versioned by `avatarAt`; without one —
+ * /api/users/:id/avatar`, any signed-in account), versioned by `avatarAt`; without one —
  * or when the image fails to load — the first letters of its name. Used by the
  * sidebar's account row, its workspace owner groups, Settings → Account, the
  * Users page and its editor, the pool board and member picker, and System
@@ -23,7 +23,7 @@ export function UserAvatar({
 }: {
   name: string;
   avatarAt?: string | null;
-  /** Another account's (staff only); omitted = the signed-in account's own. */
+  /** Another account's; omitted = the signed-in account's own. */
   userId?: number;
   /** How many letters of the name stand in for a missing picture. */
   letters?: number;