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/ThemeContext.tsx

@@ -0,0 +1,51 @@
+import { createContext, useContext, useEffect, useState } from 'react';
+import { useSQLiteContext } from 'expo-sqlite';
+import { getSetting, setSetting } from '@/db/queries';
+import { autoKey, PALETTES, type PaletteKey, type Theme } from '@/theme';
+
+type ThemeCtx = {
+  theme: Theme;
+  paletteKey: PaletteKey;
+  setPaletteOverride: (key: PaletteKey) => void;
+};
+
+const ThemeContext = createContext<ThemeCtx>({
+  theme: PALETTES.default,
+  paletteKey: 'auto',
+  setPaletteOverride: () => {},
+});
+
+export function ThemeProvider({ children }: { children: React.ReactNode }) {
+  const db = useSQLiteContext();
+  const [paletteKey, setPaletteKey] = useState<PaletteKey>('auto');
+
+  useEffect(() => {
+    getSetting(db, 'palette_override').then(val => {
+      if (val) setPaletteKey(val as PaletteKey);
+    });
+  // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+
+  function setPaletteOverride(key: PaletteKey) {
+    setPaletteKey(key);
+    setSetting(db, 'palette_override', key);
+  }
+
+  const resolved = paletteKey === 'auto' ? autoKey() : paletteKey;
+  const theme = PALETTES[resolved as keyof typeof PALETTES] ?? PALETTES.default;
+
+  return (
+    <ThemeContext.Provider value={{ theme, paletteKey, setPaletteOverride }}>
+      {children}
+    </ThemeContext.Provider>
+  );
+}
+
+export function useTheme(): Theme {
+  return useContext(ThemeContext).theme;
+}
+
+export function usePaletteControl(): Pick<ThemeCtx, 'paletteKey' | 'setPaletteOverride'> {
+  const { paletteKey, setPaletteOverride } = useContext(ThemeContext);
+  return { paletteKey, setPaletteOverride };
+}