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/playwright.config.ts

@@ -5,7 +5,7 @@ import { defineConfig, devices } from '@playwright/test';
  *
  * Assumes:
  *   - Next.js web app running on http://localhost:3000
- *   - NestJS gateway running on http://localhost:4000
+ *   - NestJS gateway running on http://localhost:14242
  *
  * Run with:   pnpm --filter @mosaic/web test:e2e
  */