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>

packages/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@mosaic/cli",
-  "version": "0.0.13",
+  "version": "0.0.14",
   "repository": {
     "type": "git",
     "url": "https://git.mosaicstack.dev/mosaic/mosaic-stack.git",