docs: port to VitePress

Things that happen in this shameless squash:
- Removed 404 page
  - It doesn't work in VitePress and making it work in VitePress needs
    some invasive hack in the theme that I'm not willing to do
  - The default is more than enough, though
- Moved consoleVersionSelect include to another directory
  - This avoids being uploaded to Crowdin for translation
- Inline all SafeB9SInstaller includes
  - Not only do parameterized includes not work, but if/else statements
    don't work at all
- The sysupdate include parameter hasn't been used since MSET9, so it
  actually works just fine without any parameters. Hooray(?)
- Move mset9-chorus to an include, that logic doesn't work in VitePress
- Removed Get Started button from homepage, it breaks translations
- Tables in get-started are now shown by default; it seems VitePress really does
  not want us to use inline script. So we cannot enable it upon
  realizing that the browser is JS capable
- Include parameters are now in frontmatter to allow translation
- Hacked in a bunch of CSS values kanged from the old theme to make it
  look not stupid
- Drop headers down one level to make table of contents work

docs/_internal/consoleVersionSelect.html

@@ -1,4 +1,4 @@
-<table id="modeltable" class="modeltable" style="display:none">
+<table id="modeltable" class="modeltable">
   <thead>
     <th><div align="center">Old 3DS/2DS</div></th>
     <th><div align="center">New 3DS/2DS</div></th>
@@ -8,7 +8,7 @@
     <td> <img class="tableimage" src="/images/new3ds.png" alt="old 3DS"> <img class="tableimage" src="/images/new3dsxl.png" alt="old 3DS"> <img class="tableimage" src="/images/new2dsxl.png" alt="old 3DS"><br><br><input type="radio" name="checkbox" id="new3DS"></td>
   </tbody>
 </table>
-<div id="selectversion" class="selectversion" style="display:none">
+<div id="selectversion" class="selectversion">
     <br>
     <select id="major">
       <option>11</option>
@@ -108,14 +108,7 @@
     <input type="button" onclick="redirect()" value="Confirm">
 </div>
 
-<script>
-document.getElementById("modeltable").style.display = "block";
-document.getElementById("selectversion").style.display = "block";
-</script>
-
-<p id="result_noneSelected" style="display:none">{{ include.noneSelected }}</p>
-<p id="result_invalidVersion" style="display:none">{{ include.invalidVersion }}</p>
-
-<script src="/assets/js/selecting.js"></script>
+<p id="result_noneSelected" style="display:none">{{ $frontmatter.noneSelected }}</p>
+<p id="result_invalidVersion" style="display:none">{{ $frontmatter.invalidVersion }}</p>
 
 <noscript>Please enable JavaScript to continue with the guide.</noscript>