ideas: add Ideas page, nav link; remove feedback button from About

New /ideas/ page with Svelte component: card list sorted by votes,
inline submit form, optimistic vote toggling, delete for own/admin.
Bug report link moved to bottom of Ideas page. Feedback button removed
from About page.

site/src/layouts/Base.astro

@@ -221,6 +221,7 @@ try {
             <a href={`${baseUrl}convert/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Convert</a>
           )}
           <a href={`${baseUrl}segments/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Segments</a>
+          <a href={`${baseUrl}ideas/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">Ideas</a>
           <a id="nav-about" href={`${baseUrl}about/`} class="text-sm text-zinc-400 hover:text-white transition-colors shrink-0">About</a>
           {wikiUrl && (
             <a id="nav-wiki" href={wikiUrl} style="display:none"