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/structured/52-the-conclusion.json

@@ -0,0 +1,14 @@
+{
+  "chapter_id": "52",
+  "slug": "the-conclusion",
+  "title": "The Conclusion",
+  "time_range_sec": [14730, 14810],
+  "summary": "Closing remarks for the Spanish fundamentals series. The narrator emphasizes that the series teaches how to THINK in Spanish (not just speak), explains the deliberate fast-paced format, and encourages learners to use these fundamentals as the basis for whatever mastery method fits them.",
+  "suggested_grammar_note_id": null,
+  "rules": [],
+  "examples": [],
+  "vocab": [],
+  "conjugation_tables": [],
+  "exercises": [],
+  "caveats": "Outro chapter only — no grammar content."
+}