feat(watchlist): dockable in the Main tab; sticky filters; Needed-only hides worked lines

The watchlist joins the Main-tab pane list (Settings → Main view), rendered in
a card like the other docked panels.

The three filters persist across tab switches — the component unmounts on every
switch, and filters that reset each time are filters nobody trusts.

Needed-only now hides the worked SPOT LINES as well as the all-worked cards,
which is DXHunter's own Not-Worked behaviour and the reported complaint: a
filter that says needed and still lists five green Worked rows answers a
different question than the one asked.

The add-row checkbox is relabelled 'as contest' — it marks the entry being
ADDED, and read as a filter beside the All/DX/Contest buttons it looked
redundant.

frontend/src/components/SettingsModal.tsx

@@ -1086,7 +1086,7 @@ function RelayAutoPanel() {
 // panes. The first two are the view; the third and fourth can be left empty, and
 // an empty one is not drawn at all. Per-profile (stored via SetUIPref, which is
 // profile-prefixed). Self-contained so it owns its async-loaded state.
-const MAIN_PANE_VALUES = ['map1', 'map2', 'cluster', 'worked', 'recent', 'netcontrol', 'decodes'];
+const MAIN_PANE_VALUES = ['map1', 'map2', 'cluster', 'worked', 'recent', 'netcontrol', 'decodes', 'watchlist'];
 const PANE_NONE = 'none';
 function MainViewPanes({ onChanged, flexAvailable, icomAvailable, yaesuAvailable, elecraftAvailable, tciAvailable }: { onChanged?: (side: 'left' | 'right' | 'p3' | 'p4' | 'layout', value: string) => void; flexAvailable?: boolean; icomAvailable?: boolean; yaesuAvailable?: boolean; elecraftAvailable?: boolean; tciAvailable?: boolean }) {
   const { t } = useI18n();