Add webapp subproject (Vite + TypeScript + Web Components)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

webapp/src/main.ts

@@ -0,0 +1,27 @@
+import './components/app-shell'
+import './components/login-page'
+import './components/days-page'
+import './components/day-detail-page'
+import './components/track-map'
+import { route, startRouter } from './router'
+
+const app = document.getElementById('app')!
+app.innerHTML = '<app-shell></app-shell>'
+
+const shell = app.querySelector('app-shell') as HTMLElement & { setPage: (el: HTMLElement) => void }
+
+route('/login', () => {
+  shell.setPage(document.createElement('login-page'))
+})
+
+route('/days', () => {
+  shell.setPage(document.createElement('days-page'))
+})
+
+route('/days/:date', ({ date }) => {
+  const el = document.createElement('day-detail-page') as HTMLElement & { date: string }
+  el.date = date
+  shell.setPage(el)
+})
+
+startRouter()