Add login form template

[Sana9058]

This PR adds a new login form template to the templates/html directory.

The template follows the existing project structure and provides a clean, reusable login form for the login page.

Closes #176

[Schlaumeier5]

At the moment, we need a little script to override the form behavior, you can look here:

student-database/src/main/resources/html/site/login.html

Lines 18 to 35 in 295d0e6

	<script>
	document.getElementById("loginForm").addEventListener("submit", async (e) => {
	e.preventDefault();
	let formData = new FormData(e.target);
	let response = await fetch("/login", {
	method: "POST",
	body: new URLSearchParams(formData),
	credentials: "include"
	});
	if (response.ok) {
	window.location.href = "/dashboard";
	} else {
	alert("Falsches Passwort!");
	}
	});
	</script>

[Schlaumeier5]

Looks nice, can you add the script from site/login.html and use the template in site/login.html and site/index.html (replace the code there with "%[login]%"
Thank you for your help!

[Sana9058]

@Schlaumeier5 Thanks for the suggestion!
I’ve moved the login script into the login template and updated site/login.html and site/index.html to use %{login}% as requested.

[Schlaumeier5]

Looks nice, tyvm :)