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/notes/01-the-introduction.md

@@ -0,0 +1,13 @@
+# 01. The Introduction
+
+> Source: [video link](https://youtube.com/watch?v=YHDZSHCt1DE&t=0s)
+
+A brief introduction to the 4-hour mega-compilation video. The author explains that this is a stitched-together collection of every previous Spanish-fundamentals video on his channel, covering every concept needed to build a working basis in Spanish.
+
+## Key Rules
+- The video is a single long compilation; quality (audio level, pacing) varies between original videos.
+- Two topics are intentionally omitted because they're considered self-explanatory or covered elsewhere: verbs like *gustar*, the difference between *qué* and *cuál*, and the difference between *c* and *qu*.
+- Watch all the way through and the author closes with a short conclusion explaining the editorial choices.
+
+## Notes & Gotchas
+- Some segments will contain phrases like "this concept is for a future video" — that wording is an artifact of the original standalone uploads, not a missing chapter here.