fix(setup): persist setup_completed flag to prevent repeated first-time notice

After running ccs setup with local proxy mode, the CLI was still showing
the first-time install notice because isFirstTimeInstall() only checked
for user-created content (profiles, accounts, variants, etc.). When user
chose "Local" mode and skipped API profiles, config had empty objects,
causing all checks to return false.

Added setup_completed flag to UnifiedConfig interface and set it to true
when setup wizard completes. isFirstTimeInstall() now checks this flag
first.

src/commands/setup-command.ts

@@ -132,6 +132,11 @@ export function isFirstTimeInstall(): boolean {
       return false;
     }
 
+    // If setup wizard was completed, NOT first-time install
+    if (loaded.setup_completed) {
+      return false;
+    }
+
     // Check for any meaningful configuration in unified config
     const hasProfiles = Object.keys(loaded.profiles || {}).length > 0;
     const hasAccounts = Object.keys(loaded.accounts || {}).length > 0;
@@ -370,6 +375,7 @@ async function runSetupWizard(force: boolean = false): Promise<void> {
     }
 
     // Save config
+    config.setup_completed = true;
     saveUnifiedConfig(config);
 
     // Final summary

src/config/unified-config-types.ts

@@ -521,6 +521,8 @@ export const DEFAULT_DASHBOARD_AUTH_CONFIG: DashboardAuthConfig = {
 export interface UnifiedConfig {
   /** Config version (7 for quota management) */
   version: number;
+  /** Flag indicating setup wizard has been completed */
+  setup_completed?: boolean;
   /** Default profile name to use when none specified */
   default?: string;
   /** Account-based profiles (isolated Claude instances) */