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/TASKS-TUI_Improvements.md

@@ -93,7 +93,7 @@ packages/cli/src/tui/
 cd /home/jwoltje/src/mosaic-mono-v1-worktrees/tui-improvements
 pnpm --filter @mosaic/cli exec tsx src/cli.ts tui
 # or after build:
-node packages/cli/dist/cli.js tui --gateway http://localhost:4000
+node packages/cli/dist/cli.js tui --gateway http://localhost:14242
 ```
 
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