feat: unified NOFXi — one system, one port, one UI

Key changes:
- Agent API routes (/api/agent/*) registered directly on NOFX's :8080 server
- No more separate :8900 port — everything on :8080
- AgentChatPage.tsx added to React frontend
- Agent tab (🤖 Agent) added to navigation bar, set as DEFAULT page
- Branding: NOFX → NOFXi everywhere (title, header, branding.ts, i18n)
- Default landing page is now Agent chat, not competition

This is THE change: there is no more 'NOFX' vs 'NOFXi'.
Users open localhost:8080, they see NOFXi.
Agent chat is the first thing they see.
All other pages (Traders, Dashboard, Strategy, Data) are still there.

One binary. One port. One product. NOFXi.

web/src/constants/branding.ts

@@ -56,8 +56,8 @@ export const OFFICIAL_LINKS = {
 
 // Brand watermark component data
 export const BRAND_INFO = {
-  name: 'NOFX',
-  tagline: 'AI Trading Platform',
+  name: 'NOFXi',
+  tagline: 'AI Trading Agent',
   version: '1.0.0',
   // Links embedded in multiple formats for redundancy
   social: {