feat: show referral opt-in hint after wallet set (when disabled)

JSON output includes referralHint with explanation.
CLI output shows gray hint line. Only appears when referrals are off.
Clearly marked as optional with "no extra fees" note.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Hiksang

src/commands/wallet.ts

@@ -468,9 +468,15 @@ export function registerWalletCommands(program: Command, isJson: () => boolean)
         }
       }
 
+      const settings = loadSettings();
+      const referralHint = !settings.referrals
+        ? { referrals: false, hint: "Optional: 'perp settings referrals on' to support perp-cli development (no extra fees — exchange rebates only)" }
+        : undefined;
+
       if (isJson()) return printJson(jsonOk({
         exchange: resolved, address, envFile: ENV_FILE, default: !!opts.default,
         ...(resolved === "lighter" && { lighterApiKey: lighterApiSetup }),
+        ...(referralHint && { referralHint }),
       }));
 
       console.log(chalk.green(`\n  ${resolved} configured.`));
@@ -485,6 +491,10 @@ export function registerWalletCommands(program: Command, isJson: () => boolean)
           console.log(chalk.gray(`  You can retry: perp -e lighter manage setup-api-key`));
         }
       }
+      if (!settings.referrals) {
+        console.log(chalk.gray(`  Optional: ${chalk.cyan("perp settings referrals on")} to support perp-cli development`));
+        console.log(chalk.gray(`  (no extra fees — exchange rebates only)`));
+      }
       console.log();
     });