feat(web): replace the sidebar with a full-width top bar

- One top bar for every screen size: feeds as chips with unread counts,
  Focus mode, theme, add feed, and a menu for managing feeds, OPML export
  and logout. The article grid now uses the full page width.
- New "Mes flux" dialog to rename or delete feeds (was hidden behind
  hover actions in the sidebar); feeds that fail to update are flagged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/pages/DashboardPage.tsx

@@ -226,7 +226,7 @@ export function DashboardPage({ selectedFeedId, hidden }: DashboardPageProps) {
 
     return (
         <main ref={mainRef} className={`flex-1 overflow-y-auto bg-carbon relative ${hidden ? 'hidden' : ''}`} aria-busy={isFetching}>
-            <div className="max-w-[1400px] mx-auto px-4 sm:px-6 md:px-12 py-8 md:py-12">
+            <div className="max-w-[1400px] mx-auto px-4 sm:px-6 md:px-12 py-6 md:py-8">
                 <header className="mb-8 flex flex-wrap items-end justify-between gap-x-6 gap-y-4">
                     <div className="min-w-0">
                         <h1 className="text-3xl md:text-4xl font-serif text-paper-white tracking-tight break-words">{heading}</h1>