fix: palette changes now propagate immediately via ThemeContext

Replace useSetting()-based useTheme() with a React context (ThemeProvider
+ useTheme/usePaletteControl). The context holds palette key in state so
pressing a palette button in Settings re-renders all screens instantly.
Persists to SQLite and reloads the stored value on mount.

mobile/app/(tabs)/settings.tsx

@@ -5,7 +5,8 @@ import {
   Text, TextInput, View,
 } from 'react-native';
 import { deleteRemoteActivities, getSetting, setSetting, useSetting } from '@/db/queries';
-import { PALETTES, type PaletteKey, useTheme } from '@/theme';
+import { PALETTES, type PaletteKey } from '@/theme';
+import { useTheme, usePaletteControl } from '@/ThemeContext';
 
 export default function SettingsScreen() {
   const db = useSQLiteContext();
@@ -24,8 +25,7 @@ export default function SettingsScreen() {
   const [syncUpload,  setSyncUpload]  = useState(storedSyncUpload);
   const [saved,       setSaved]       = useState(false);
   const theme = useTheme();
-  const storedPalette = (useSetting('palette_override') ?? 'auto') as PaletteKey;
-  const [palette, setPalette] = useState<PaletteKey>(storedPalette);
+  const { paletteKey: palette, setPaletteOverride } = usePaletteControl();
 
   const [password,    setPassword]    = useState('');
   const [connecting,  setConnecting]  = useState(false);
@@ -225,10 +225,7 @@ export default function SettingsScreen() {
                 active={palette === key}
                 accent={keyAccent}
                 dim={keyDim}
-                onPress={() => {
-                  setPalette(key);
-                  setSetting(db, 'palette_override', key);
-                }}
+                onPress={() => setPaletteOverride(key)}
               />
             );
           })}