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/package-lock.json

@@ -12,6 +12,7 @@
         "@tanstack/react-query": "^5.51.0",
         "@tanstack/react-virtual": "^3.14.3",
         "clsx": "^2.1.1",
+        "flag-icons": "^7.5.0",
         "hls.js": "^1.6.16",
         "i18next": "^23.11.5",
         "lucide-react": "^0.408.0",
@@ -1809,6 +1810,12 @@
         "node": ">=8"
       }
     },
+    "node_modules/flag-icons": {
+      "version": "7.5.0",
+      "resolved": "https://registry.npmjs.org/flag-icons/-/flag-icons-7.5.0.tgz",
+      "integrity": "sha512-kd+MNXviFIg5hijH766tt+3x76ele1AXlo4zDdCxIvqWZhKt4T83bOtxUOOMlTx/EcFdUMH5yvQgYlFh1EqqFg==",
+      "license": "MIT"
+    },
     "node_modules/fraction.js": {
       "version": "5.3.4",
       "resolved": "https://registry.npmjs.org/fraction.js/-/fraction.js-5.3.4.tgz",