Add dynamic subpath support (#1011)

* Add dynamic subpath support for WebUI

- Add SubpathConfig utility for server-side subpath detection
- Configure React Router basename from server config
- Update API base URL handling for subpath compatibility
- Fix asset loading with relative paths
- Add VITE_SUBPATH environment variable for development
- Update locales and manifest paths for subpath support

Closes #174

* Move VITE_SUBPATH interface to vite-env.d.ts

* Ensure production bundle always uses relative base

.env.template

@@ -3,6 +3,10 @@ ALLOWED_HOSTS =
 
 VITE_SERVER_URL_DEFAULT = http://localhost:4567
 
+# Optional: Set a subpath for the WebUI during development (e.g. /suwayomi)
+# For production use, configure webUISubpath in server settings instead
+# VITE_SUBPATH = /suwayomi
+
 CODEGEN_SERVER_URL_GQL = http://localhost:4567/api/graphql
 
 GITHUB_TOKEN =