feat: seasonal race palette (Giro/Tour/Vuelta) + mobile picker

- theme.ts: useTheme() hook with race calendar (May–Sep windows),
  auto-detects Giro/Tour/Vuelta by date; stores override in SQLite
- All screens (feed, import, activity, tab bar) now use accent/dim
  from useTheme() instead of hardcoded #60a5fa
- Settings: Palette section with Auto/Default/Giro/Tour/Vuelta buttons
  to override the auto-detected palette for testing

mobile/app/(tabs)/import.tsx

@@ -6,6 +6,7 @@ import { Pressable, ScrollView, StyleSheet, Text, View } from 'react-native';
 import { insertActivity } from '@/db/queries';
 import { PyodideWebView } from '@/extraction/PyodideWebView';
 import { extractFile } from '@/extraction/extractActivity';
+import { useTheme } from '@/theme';
 
 const FIT_EXTENSIONS  = ['.fit', '.fit.gz'];
 const OTHER_EXTENSIONS = ['.gpx', '.tcx', '.gpx.gz', '.tcx.gz'];
@@ -19,6 +20,7 @@ type ImportState =
 
 export default function ImportScreen() {
   const db = useSQLiteContext();
+  const theme = useTheme();
   const [state, setState] = useState<ImportState>({ status: 'idle' });
 
   async function pickFile() {
@@ -143,7 +145,7 @@ export default function ImportScreen() {
 
       <Text style={styles.body}>
         Import a FIT, GPX, or TCX file — extracted on your device, nothing uploaded.
-        You can also import a pre-extracted BAS <Text style={styles.code}>.json</Text> file directly.
+        You can also import a pre-extracted BAS <Text style={[styles.code, { color: theme.accent }]}>.json</Text> file directly.
       </Text>
 
       <Pressable
@@ -157,7 +159,7 @@ export default function ImportScreen() {
 
       {state.status === 'loading' && (
         <View style={styles.statusBox}>
-          <Text style={styles.statusMsg}>{state.msg}</Text>
+          <Text style={[styles.statusMsg, { color: theme.accent }]}>{state.msg}</Text>
           <Text style={styles.statusHint}>
             First run downloads ~35 MB (Python runtime + packages). Subsequent runs are instant.
           </Text>