Move to Leptos 0.7.7 and update example

[modeckrus]

[wiseaidev]

Hey @modeckrus,

Thanks for the effort! LGTM! Unfortunately, I lost access to this repo and I'm no longer a maintainer, so I can't merge this PR. Lemme check with @Belacosaur to see if he can add me back as a core maintainer or transfer ownership to @opensass.