feat: add p/demo/mux

[moul]

Add a simple mux/router system for Render().
Update the p/demo/blog package accordingly.
Inspired by #866 which aims to offer an all-in-one framework.

Not sure if should be p/demo/mux or p/demo/router. Idea?

Contributors Checklist

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests

Maintainers Checklist

• Checked that the author followed the guidelines in CONTRIBUTING.md
• Checked the conventional-commit (especially PR title and verb, presence of BREAKING CHANGE: in the body)
• Ensured that this PR is not a significant change or confirmed that the review/consideration process was appropriate for the change

[harry-hov]

Just add gno.mod file. Rest LGTM 💯

[moul]

Just add gno.mod file. Rest LGTM 💯

$ moul in 🌐 crux in  2 ~/g/s/g/g/g/e/g/p/demo/ui  dev/moul/mux   via  v1.20.3 
❯ gno mod init
USAGE
  mod <command>

SUBCOMMANDS
  download  Download modules to local cache

ohhhh :)

---

Edit(@harry-hov): Soon!

[harry-hov]

Just one last thing. Add gno.land/p/demo/mux as dependency in p/demo/blog/gno.mod

PS: please bear until gno mod tidy :)

[moul]

done

[harry-hov]

Merging this for now. If we come up with a better name, we can change it in another PR.