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/components/common/HeaderBar.tsx

@@ -6,6 +6,7 @@ import { t, type Language } from '../../i18n/translations'
 import { OFFICIAL_LINKS } from '../../constants/branding'
 
 type Page =
+  | 'agent'
   | 'competition'
   | 'traders'
   | 'trader'
@@ -93,6 +94,7 @@ export default function HeaderBar({
             {(() => {
               // Define all navigation tabs
               const navTabs: { page: Page; path: string; label: string; requiresAuth: boolean }[] = [
+                { page: 'agent', path: '/agent', label: language === 'zh' ? '🤖 Agent' : '🤖 Agent', requiresAuth: false },
                 { page: 'data', path: '/data', label: language === 'zh' ? '数据' : language === 'id' ? 'Data' : 'Data', requiresAuth: false },
                 { page: 'strategy-market', path: '/strategy-market', label: language === 'zh' ? '策略市场' : language === 'id' ? 'Pasar' : 'Market', requiresAuth: true },
                 { page: 'traders', path: '/traders', label: t('configNav', language), requiresAuth: true },
@@ -334,6 +336,7 @@ export default function HeaderBar({
               <div className="flex flex-col gap-6 mb-12">
                 {(() => {
                   const navTabs: { page: Page; path: string; label: string; requiresAuth: boolean }[] = [
+                    { page: 'agent', path: '/agent', label: '🤖 Agent', requiresAuth: false },
                     { page: 'data', path: '/data', label: language === 'zh' ? '数据' : language === 'id' ? 'Data' : 'Data', requiresAuth: false },
                     { page: 'strategy-market', path: '/strategy-market', label: language === 'zh' ? '策略市场' : language === 'id' ? 'Pasar' : 'Market', requiresAuth: true },
                     { page: 'traders', path: '/traders', label: t('configNav', language), requiresAuth: true },