feat(ui): favicon, dynamic tab title, clickable logo, styled module headers

Session-close cosmetics:
1. Favicon — an 'S' monogram (indigo→violet rounded square, path-drawn so it's font-independent)
   at public/favicon.svg, linked in index.html (tab had none before).
2. Dynamic document.title — reflects the current module ('Downloads · Siftlode'); Feed = brand
   only; an open channel page shows the channel name. Shared pageTitleKey() in lib/pageMeta.ts
   keeps the tab title and the top-bar header in lockstep.
3. The 'Siftlode' logo already navigated to Feed but read as static text — added a hover
   background + cursor affordance so it's clearly clickable.
4. Module header — new shared PageTitle component (used by every non-feed module via Header) with
   a tracked small-caps 'eyebrow' + leading accent dot (user-picked style B), styled in one place.
Verified in a real browser: favicon served (image/svg+xml), title updates per module, logo→feed,
header restyled; no console errors.

frontend/src/components/Header.tsx

@@ -2,6 +2,8 @@ import { useTranslation } from "react-i18next";
 import { Search, X, Youtube } from "lucide-react";
 import type { FeedFilters, Me } from "../lib/api";
 import type { Page } from "../lib/urlState";
+import { pageTitleKey } from "../lib/pageMeta";
+import PageTitle from "./PageTitle";
 
 // Contextual top bar over the content column. Primary navigation, account and the per-user sync
 // status live in the left NavSidebar; the feed's scope toggle now lives in the filter sidebar.
@@ -72,26 +74,8 @@ export default function Header({
           )}
         </div>
       ) : (
-        <div className="flex-1 text-center text-sm font-semibold">
-          {page === "stats"
-            ? t("header.usageStats")
-            : page === "playlists"
-              ? t("header.account.playlists")
-              : page === "settings"
-                ? t("settings.title")
-                : page === "scheduler"
-                  ? t("header.scheduler")
-                  : page === "config"
-                    ? t("header.configuration")
-                    : page === "users"
-                      ? t("header.users")
-                      : page === "notifications"
-                        ? t("inbox.navLabel")
-                        : page === "messages"
-                          ? t("messages.navLabel")
-                          : page === "downloads"
-                            ? t("downloads.navLabel")
-                            : t("header.channelManager")}
+        <div className="flex-1 flex justify-center">
+          <PageTitle label={t(pageTitleKey(page))} />
         </div>
       )}
     </header>

frontend/src/components/NavSidebar.tsx

@@ -256,8 +256,9 @@ export default function NavSidebar({
         {!collapsed && (
           <button
             onClick={() => setPage("feed")}
-            className="text-lg font-bold tracking-tight select-none"
+            className="text-lg font-bold tracking-tight select-none cursor-pointer rounded-md -mx-1 px-1 hover:bg-card hover:opacity-90 transition"
             title={t("header.feed")}
+            aria-label={t("header.feed")}
           >
             Sift<span className="text-accent">lode</span>
           </button>

frontend/src/components/PageTitle.tsx

@@ -0,0 +1,11 @@
+// The centered module title in the top bar. Every non-feed module renders through this one
+// component, so its styling lives in a single place. Design element (user-picked): a tracked
+// small-caps "eyebrow" with a leading accent dot.
+export default function PageTitle({ label }: { label: string }) {
+  return (
+    <span className="inline-flex items-center gap-2 text-xs font-semibold uppercase tracking-[0.16em] text-fg">
+      <span className="w-1.5 h-1.5 rounded-full bg-accent shrink-0" />
+      {label}
+    </span>
+  );
+}