fix: Handle .mod files for realms in gnoweb (#2278)

Fixes #2277 to render `.mod` files for realms

Before:

![image](https://github.com/gnolang/gno/assets/49811529/6ef8e4a0-76b7-4a2c-9720-9158e9d67d08)

After:

![image](https://github.com/gnolang/gno/assets/49811529/20d0876d-eee6-4c3b-a74f-22c0314f074e)



<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

gno.land/pkg/gnoweb/gnoweb.go

@@ -110,7 +110,7 @@ func MakeApp(logger *slog.Logger, cfg Config) gotuna.App {
 	}
 	// realm routes
 	// NOTE: see rePathPart.
-	app.Router.Handle("/r/{rlmname:[a-z][a-z0-9_]*(?:/[a-z][a-z0-9_]*)+}/{filename:(?:.*\\.(?:gno|md|txt)$)?}", handlerRealmFile(logger, app, &cfg))
+	app.Router.Handle("/r/{rlmname:[a-z][a-z0-9_]*(?:/[a-z][a-z0-9_]*)+}/{filename:(?:.*\\.(?:gno|md|txt|mod)$)?}", handlerRealmFile(logger, app, &cfg))
 	app.Router.Handle("/r/{rlmname:[a-z][a-z0-9_]*(?:/[a-z][a-z0-9_]*)+}", handlerRealmMain(logger, app, &cfg))
 	app.Router.Handle("/r/{rlmname:[a-z][a-z0-9_]*(?:/[a-z][a-z0-9_]*)+}:{querystr:.*}", handlerRealmRender(logger, app, &cfg))
 	app.Router.Handle("/p/{filepath:.*}", handlerPackageFile(logger, app, &cfg))