Add 13 new grammar notes with 1010 exercises from video extraction

Scraped a 4h Spanish fundamentals YouTube video (transcript + OCR on
14810 frames), extracted structured content across 52 chapters, and
generated fill-in-the-blank quizzes for every grammar topic.

- 13 new GrammarNote entries (articles, possessives, demonstratives,
  greetings, poder, al/del, prepositional pronouns, irregular yo,
  stem-changing, stressed possessives, present/future perfect, present
  indicative conjugation)
- 1010 generated exercises across all 36 grammar notes (new + existing)
- Fix tense guide parser to handle unnumbered *Usages* blocks
- Rewrite 6 broken tense guide bodies (imperative, subj pluperfect,
  subj future) with numbered usage format
- Bump courseDataVersion 5→6 with TenseGuide refresh on upgrade
- Add docs/spanish-fundamentals/ with raw transcripts, polished notes,
  structured JSON, and exercise data

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/spanish-fundamentals/exercises/seed/future-perfect-tense.json

@@ -0,0 +1,58 @@
+[
+  {
+    "sentence": "Para el lunes, yo _____ terminado. (haber)",
+    "correct": "habré",
+    "distractor": "habría",
+    "explanation": "Future of haber, yo = habré.",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  },
+  {
+    "sentence": "Dentro de un año, tú _____ dejado tu trabajo.",
+    "correct": "habrás",
+    "distractor": "habrías",
+    "explanation": "Tú future of haber = habrás.",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  },
+  {
+    "sentence": "Para esa fecha, John _____ recibido muchas ofertas.",
+    "correct": "habrá",
+    "distractor": "habría",
+    "explanation": "Él future of haber = habrá.",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  },
+  {
+    "sentence": "Nosotros _____ llegado para mañana.",
+    "correct": "habremos",
+    "distractor": "habríamos",
+    "explanation": "Nosotros future of haber = habremos (no accent).",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  },
+  {
+    "sentence": "Ellos _____ comido dentro de dos horas.",
+    "correct": "habrán",
+    "distractor": "han",
+    "explanation": "Future perfect needs habrán, not present.",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  },
+  {
+    "sentence": "Para diciembre, ella habrá _____ . (volver)",
+    "correct": "vuelto",
+    "distractor": "volvido",
+    "explanation": "Volver has irregular participle 'vuelto'.",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  },
+  {
+    "sentence": "By summer, I will have learned = Para el verano, yo _____ aprendido.",
+    "correct": "habré",
+    "distractor": "he",
+    "explanation": "Future perfect uses habré, not he (present perfect).",
+    "source_chapter": "42",
+    "source_title": "Future Perfect Tense"
+  }
+]