Make octave-reading source attribution bilingual

The heading above each Matins octave reading was a bare Latin string
(e.g. "Sermo sancti Bernárdi Abbátis") rendered as-is in both the
Latin and English columns, since the app shows both languages side
by side rather than toggling. Widen OctaveReadingText.source and the
lesson part's label to carry per-language text, and render it as its
own lang-columns row like the body text beneath it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L3wxvz3mPXiHxkPB5JpnmD

tests/propers/octave-readings.test.ts

@@ -4,7 +4,8 @@ import { getOctaveReading } from '../../src/propers';
 describe('getOctaveReading', () => {
   it('resolves a real reading for a day that has one, collapsed into one continuous text', () => {
     const reading = getOctaveReading('st-lawrence', 2);
-    expect(reading?.source).toBe('Sermo sancti Augustíni Epíscopi.');
+    expect(reading?.source.la).toBe('Sermo sancti Augustíni Epíscopi.');
+    expect(reading?.source.en).toBe('Sermon of St. Augustine, Bishop');
     expect(reading?.text.la).toContain('Beatissimi Laurentii Martyris');
     expect(reading?.text.en).toContain('most blessed Martyr, Lawrence');
     expect(reading?.status.la).toBe('verified');