Fix design-review findings: self-linking nav, colour reuse, badge clash

From a frontend-design skill review of all pages, after last session's
chrome changes (top nav, all-tabs nav, header download row):

- The top/closing fastext nav now mutes the entry matching the current
  page (.fastext-here) instead of rendering a link to the page you're
  already on.
- Colour in fastext is reserved for the four entries that still carry
  a real keyboard shortcut (r/g/y/c); the other four render in plain
  ink instead of reusing k-red/k-green/k-yellow/k-cyan for a
  destination they don't semantically mean (e.g. Requests no longer
  shows in the app's own off-air red).
- Discover's badge slot meant "critic score" on its RT tiles and
  "release year" on its new search tiles at the same time. Search
  results (Library and Discover) now fold year/held-state into the
  sub-line instead, leaving the badge exclusively for critic score.
- System's Transmission rows now carry a small ↗ glyph, since they
  silently changed from in-app navigation to opening each service's
  own UI in a new tab with no visual cue.
- SABnzbd polling drops from 5s to 20s on pages that only show the
  header's download figure (everywhere but System/Activity, which
  keep 5s for their own live figures) — a number idle 95% of the time
  doesn't need second-level freshness sitewide.
- DESIGN.md's fastext description, now-current per this session's nav
  changes.

templates/system.html

@@ -14,7 +14,7 @@
     {% for name, key, svc in [('Sonarr', 'sonarr', sonarr), ('Radarr', 'radarr', radarr), ('SABnzbd', 'sabnzbd', sabnzbd),
                               ('Tautulli', 'tautulli', tautulli), ('Prowlarr', 'prowlarr', prowlarr), ('Ombi', 'ombi', ombi)] %}
     <a class="tt-row" href="{{ service_urls[key] }}" target="_blank" rel="noopener">
-      <span class="tt-row-name">{{ name }}</span>
+      <span class="tt-row-name">{{ name }} <span class="tt-row-ext" aria-hidden="true">&#8599;</span></span>
       <span class="tt-row-body"></span>
       <span class="tt-row-val {{ 'ok' if svc.status == 'ok' else 'alert' }}">
         {{- 'ON AIR' if svc.status == 'ok' else 'OFF AIR' -}}