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.

app.py

@@ -1304,17 +1304,20 @@ def service_urls():
 
 
 # Every destination, for the top of every page but the index. Order
-# matches nav_items; the four letter keys keep the destinations they
-# always had, cycling colour for the rest since only four exist.
+# matches nav_items. Colour is semantic everywhere else in this app
+# (red = off-air, magenta = needs a decision, ...), so only the four
+# that still carry a real teletext keyboard shortcut (r/g/y/c) get a
+# colour swatch; the rest render in plain ink rather than borrowing
+# one of the four colours for a destination it doesn't mean.
 FULL_FASTEXT = [
     ("k-red",    "r", "100", "Index",    "/"),
-    ("k-cyan",   "",  "101", "Watch",    "/watch"),
+    ("",         "",  "101", "Watch",    "/watch"),
     ("k-green",  "g", "102", "Library",  "/library"),
     ("k-yellow", "y", "103", "Discover", "/discover"),
-    ("k-red",    "",  "104", "Requests", "/requests"),
+    ("",         "",  "104", "Requests", "/requests"),
     ("k-cyan",   "c", "105", "System",   "/system"),
-    ("k-green",  "",  "106", "Activity", "/activity"),
-    ("k-yellow", "",  "900", "Settings", "/settings"),
+    ("",         "",  "106", "Activity", "/activity"),
+    ("",         "",  "900", "Settings", "/settings"),
 ]
 
 # The index's own closing row: just the four letter keys, since the