refactor: unify into single muyue binary with embedded desktop mode

- Merge muyue + muyue-desktop into one binary (13MB)
- `muyue` starts TUI, `muyue desktop` launches web UI in browser
- Move frontend from cmd/muyue-desktop/frontend/ to web/ (standard Go layout)
- Add web/embed.go with //go:embed all:dist for frontend assets
- Add internal/desktop/ package (server, browser open, SPA routing, signals)
- Split internal/api/api.go into server.go + handlers.go
- Add internal/desktop/desktop.go with SPA fallback and --port/--no-open flags
- Clean package.json: remove unused @xterm/xterm, switch to ESM
- Fix vite.config.js proxy to use port 8095 for dev mode
- Add Makefile targets: frontend, desktop, dev-desktop
- Update all CI workflows: single binary build, web/ paths
- Remove cmd/muyue-desktop/ entirely

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/vite.config.js

@@ -0,0 +1,19 @@
+import { defineConfig } from 'vite'
+import react from '@vitejs/plugin-react'
+
+export default defineConfig({
+  plugins: [react()],
+  build: {
+    outDir: 'dist',
+    emptyOutDir: true,
+  },
+  server: {
+    port: 5173,
+    proxy: {
+      '/api': {
+        target: 'http://127.0.0.1:8095',
+        changeOrigin: true,
+      },
+    },
+  },
+})