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>

docs/guides/deployment.md

@@ -194,7 +194,7 @@ server {
 
     # WebSocket support (for chat.gateway.ts / Socket.IO)
     location /socket.io/ {
-        proxy_pass http://127.0.0.1:4000;
+        proxy_pass http://127.0.0.1:14242;
         proxy_http_version 1.1;
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection "upgrade";
@@ -204,7 +204,7 @@ server {
 
     # REST + auth
     location / {
-        proxy_pass http://127.0.0.1:4000;
+        proxy_pass http://127.0.0.1:14242;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
@@ -234,11 +234,11 @@ server {
 # /etc/caddy/Caddyfile
 
 your-domain.example.com {
-    reverse_proxy /socket.io/* localhost:4000 {
+    reverse_proxy /socket.io/* localhost:14242 {
         header_up Upgrade {http.upgrade}
         header_up Connection {http.connection}
     }
-    reverse_proxy localhost:4000
+    reverse_proxy localhost:14242
 }
 
 app.your-domain.example.com {
@@ -328,7 +328,7 @@ MaxRetentionSec=30day
 - Set `BETTER_AUTH_SECRET` to a cryptographically random value (`openssl rand -base64 32`).
 - Restrict `GATEWAY_CORS_ORIGIN` to your exact frontend origin — do not use `*`.
 - Run services as a dedicated non-root system user (e.g., `mosaic`).
-- Firewall: only expose ports 80/443 externally; keep 4000 and 3000 bound to `127.0.0.1`.
+- Firewall: only expose ports 80/443 externally; keep 14242 and 3000 bound to `127.0.0.1`.
 - Set `AGENT_FILE_SANDBOX_DIR` to a directory outside the application root to prevent agent tools from accessing source code.
 - If using `AGENT_USER_TOOLS`, enumerate only the tools non-admin users need.