chore: move gateway default port from 4000 to 14242

Port 4000 collides with too many dev tools (Phoenix, GraphQL tools, etc.).
Switch to 14242 — unregistered with IANA, no known conflicts, safely within
the User Ports range and outside Linux ephemeral port range (32768+).

Updates all hardcoded defaults across gateway, web client, CLI commands,
playwright config, .env.example, and docs. Bumps @mosaic/cli and
@mosaic/mosaic to 0.0.14.

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

apps/web/src/lib/api.ts

@@ -1,4 +1,4 @@
-const GATEWAY_URL = process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:4000';
+const GATEWAY_URL = process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:14242';
 
 export interface ApiRequestInit extends Omit<RequestInit, 'body'> {
   body?: unknown;

apps/web/src/lib/auth-client.ts

@@ -2,7 +2,7 @@ import { createAuthClient } from 'better-auth/react';
 import { adminClient, genericOAuthClient } from 'better-auth/client/plugins';
 
 export const authClient = createAuthClient({
-  baseURL: process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:4000',
+  baseURL: process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:14242',
   plugins: [adminClient(), genericOAuthClient()],
 });
 

apps/web/src/lib/socket.ts

@@ -1,6 +1,6 @@
 import { io, type Socket } from 'socket.io-client';
 
-const GATEWAY_URL = process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:4000';
+const GATEWAY_URL = process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:14242';
 
 let socket: Socket | null = null;