feat: Make app fully portable

- Add tauri-plugin-store for portable data storage
- Implement portable data directory (TypoGenie-Data/ next to EXE)
- Configure Rust backend to use EXE-relative paths
- Add store permissions for persistent settings
- Update README with portable badges and documentation
- Document how to build and use the portable EXE
- Zero registry, zero AppData, fully self-contained

package-lock.json

@@ -11,6 +11,7 @@
         "@tauri-apps/api": "^2.0.0",
         "@tauri-apps/plugin-dialog": "^2.0.0",
         "@tauri-apps/plugin-fs": "^2.0.0",
+        "@tauri-apps/plugin-store": "^2.4.2",
         "docx": "^8.5.0",
         "lucide-react": "^0.563.0",
         "marked": "12.0.0",
@@ -1401,6 +1402,15 @@
         "@tauri-apps/api": "^2.8.0"
       }
     },
+    "node_modules/@tauri-apps/plugin-store": {
+      "version": "2.4.2",
+      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-store/-/plugin-store-2.4.2.tgz",
+      "integrity": "sha512-0ClHS50Oq9HEvLPhNzTNFxbWVOqoAp3dRvtewQBeqfIQ0z5m3JRnOISIn2ZVPCrQC0MyGyhTS9DWhHjpigQE7A==",
+      "license": "MIT OR Apache-2.0",
+      "dependencies": {
+        "@tauri-apps/api": "^2.8.0"
+      }
+    },
     "node_modules/@types/babel__core": {
       "version": "7.20.5",
       "resolved": "https://registry.npmjs.org/@types/babel__core/-/babel__core-7.20.5.tgz",