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/por-vs-para.json

@@ -0,0 +1,82 @@
+[
+  {
+    "sentence": "Caminé _____ el parque ayer.",
+    "correct": "por",
+    "distractor": "para",
+    "explanation": "Movement through a place uses por.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Este regalo es _____ ti.",
+    "correct": "para",
+    "distractor": "por",
+    "explanation": "Recipient uses para.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Estudio mucho _____ aprobar el examen.",
+    "correct": "para",
+    "distractor": "por",
+    "explanation": "Purpose / in order to uses para.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Llegué tarde _____ el tráfico.",
+    "correct": "por",
+    "distractor": "para",
+    "explanation": "Reason / because of uses por.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Trabajé _____ ocho horas.",
+    "correct": "por",
+    "distractor": "para",
+    "explanation": "Duration uses por.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Necesito el informe _____ el lunes.",
+    "correct": "para",
+    "distractor": "por",
+    "explanation": "Deadline uses para.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Pagué cien dólares _____ esta camisa.",
+    "correct": "por",
+    "distractor": "para",
+    "explanation": "Exchange uses por.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "_____ mí, el español es fácil.",
+    "correct": "Para",
+    "distractor": "Por",
+    "explanation": "Personal opinion uses para.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Mi hermana trabaja _____ Google.",
+    "correct": "para",
+    "distractor": "por",
+    "explanation": "Employer uses para.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  },
+  {
+    "sentence": "Conducimos a 100 km _____ hora.",
+    "correct": "por",
+    "distractor": "para",
+    "explanation": "Per / rate uses por.",
+    "source_chapter": "33",
+    "source_title": "Por & Para"
+  }
+]