feat(managers): clickable links in descriptions + real SVG country flags

- linkify: bare http(s) URLs inside channel descriptions become clickable links
  (new tab, rel=noopener noreferrer) — new lib/linkify.tsx, used in the shared
  ChannelAboutContent so both the About overlay and the channel detail page get it
- Country flag: the flag EMOJI never renders on Windows/Chrome (showed the small-caps
  'hu' fallback), so swap it for a real self-hosted SVG flag via the flag-icons package;
  applies to the About overlay + the channel detail page

frontend/src/lib/linkify.tsx

@@ -0,0 +1,36 @@
+import { Fragment, type ReactNode } from "react";
+
+// A bare http(s) URL: greedy up to whitespace/<, but don't swallow a trailing sentence
+// punctuation mark (so "…see https://x.com/y." links "https://x.com/y", not the dot).
+const URL_RE = /(https?:\/\/[^\s<]+[^\s<.,!?;:)\]}"'])/g;
+
+/**
+ * Turn bare http(s) URLs inside a plain-text string into clickable links that open in a new tab
+ * (with a safe rel). Everything else is returned as text, so it composes with `whitespace-pre-wrap`
+ * (line breaks preserved). Used for channel/video descriptions where links arrive as plain text.
+ */
+export function linkify(text: string): ReactNode[] {
+  const out: ReactNode[] = [];
+  let last = 0;
+  let key = 0;
+  URL_RE.lastIndex = 0;
+  let m: RegExpExecArray | null;
+  while ((m = URL_RE.exec(text)) !== null) {
+    if (m.index > last) out.push(<Fragment key={key++}>{text.slice(last, m.index)}</Fragment>);
+    const url = m[0];
+    out.push(
+      <a
+        key={key++}
+        href={url}
+        target="_blank"
+        rel="noopener noreferrer"
+        className="text-accent hover:underline break-all"
+      >
+        {url}
+      </a>,
+    );
+    last = m.index + url.length;
+  }
+  if (last < text.length) out.push(<Fragment key={key++}>{text.slice(last)}</Fragment>);
+  return out;
+}