Make app fully portable, remove installers

- Remove MSI and NSIS installer targets, only produce vesper.exe
- Remove tauri-plugin-window-state, replace with manual window state
  save/restore to data/window-state.json next to the exe
- Redirect WebView2 user data (including localStorage) to data/
  folder next to the exe via WEBVIEW2_USER_DATA_DIR
- Nothing written to AppData, registry, or any system location
- Update README with portable usage info

package-lock.json

@@ -16,7 +16,6 @@
         "@tauri-apps/plugin-dialog": "^2.6.0",
         "@tauri-apps/plugin-fs": "^2.4.5",
         "@tauri-apps/plugin-opener": "^2",
-        "@tauri-apps/plugin-window-state": "^2.4.1",
         "daisyui": "^5.5.18",
         "framer-motion": "^12.34.0",
         "highlight.js": "^11.11.1",
@@ -2196,15 +2195,6 @@
         "@tauri-apps/api": "^2.8.0"
       }
     },
-    "node_modules/@tauri-apps/plugin-window-state": {
-      "version": "2.4.1",
-      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-window-state/-/plugin-window-state-2.4.1.tgz",
-      "integrity": "sha512-OuvdrzyY8Q5Dbzpj+GcrnV1iCeoZbcFdzMjanZMMcAEUNy/6PH5pxZPXpaZLOR7whlzXiuzx0L9EKZbH7zpdRw==",
-      "license": "MIT OR Apache-2.0",
-      "dependencies": {
-        "@tauri-apps/api": "^2.8.0"
-      }
-    },
     "node_modules/@tootallnate/quickjs-emscripten": {
       "version": "0.23.0",
       "resolved": "https://registry.npmjs.org/@tootallnate/quickjs-emscripten/-/quickjs-emscripten-0.23.0.tgz",