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

src-tauri/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "typogenie"
 version = "1.0.0"
-description = "TypoGenie - Markdown to Word document converter"
+description = "TypoGenie - Portable Markdown to Word document converter"
 authors = ["TypoGenie Contributors"]
 license = "MIT"
 repository = "https://git.lashman.live/lashman/typogenie"
@@ -23,3 +23,4 @@ tauri = { version = "2.9.5" }
 tauri-plugin-log = "2"
 tauri-plugin-dialog = "2"
 tauri-plugin-fs = "2"
+tauri-plugin-store = "2"