Preferences in Settings and a home page the user chooses

Settings gets a Preferences section: theme, default Bible, the Bible new reading
plans start in, verse layout, commentary, text size, reading width, audio
narrator (the last three stay per device; text size and narrator are now
remembered). A Home page setting (My Studies, Bible Reader or Reading Plans)
decides where the app opens and where every Home button goes; already being
there means My Studies. Back arrows are labelled Home. Tests cover every page
leading back.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/prefs.test.js

@@ -14,6 +14,11 @@ test('only known preferences with valid values are accepted', () => {
   expect(cleanPrefValue('translation', 'KJV')).toBeUndefined();
   expect(cleanPrefValue('layout', 'flow')).toBe('flow');
   expect(cleanPrefValue('commentarySource', 'tyndale')).toBe('tyndale');
+  expect(cleanPrefValue('startPage', 'reader')).toBe('reader');
+  expect(cleanPrefValue('startPage', 'admin')).toBeUndefined();
+  expect(cleanPrefValue('planTranslation', 'same')).toBe('same');
+  expect(cleanPrefValue('planTranslation', 'NASB')).toBe('NASB');
+  expect(cleanPrefValue('planTranslation', 'KJV')).toBeUndefined();
   expect(cleanPrefValue('fontSize', 2)).toBeUndefined(); // not a synced preference
 });