feat: web SPA build target + UX overhaul + public deployment setup

- Replace Electron IPC with native fetch + AbortController (VITE_VALHALLA_URL)
- Add vite.web.config.ts for standalone SPA build (npm run build:web)
- Per-mode color palettes (green/cyan/amber), RDP polygon simplification
- Interactive legend, hover popup, right-click context menu, map labels
- Toast notifications, history (last 5), auto-recalculate toggle
- Status dot, error card with retry, timing feedback, copy coordinates
- Zustand: toasts, history, hiddenLayers, autoRecalculate
- Add README.md and AGENT.md

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

src/preload/index.d.ts

@@ -3,6 +3,11 @@ import { ElectronAPI } from '@electron-toolkit/preload'
 declare global {
   interface Window {
     electron: ElectronAPI
-    api: unknown
+    api: {
+      valhallaFetch: (url: string, body: string) => Promise<string>
+      valhallaAbort: () => Promise<void>
+      getValhallaStatus: () => Promise<'ready' | 'starting' | 'error'>
+      onValhallaStatus: (cb: (status: 'ready' | 'starting' | 'error') => void) => void
+    }
   }
 }