add language learner project

Dutch and Korean (explained in English) and English (explained in Dutch)
from A1 to C1, with a Hangul level for Korean. Lessons with notes, words
and sentences generate multiple-choice, typing, sentence building, cloze,
listening and matching exercises. Endless challenges: a seeded daily
challenge, sprint, survival, mixed practice, level tests, spaced-repetition
reviews and generated drills (numbers, clock times, de/het, plurals, Dutch
and Korean conjugation, particles, Hangul reading, irregular verbs).
Progress is stored in localStorage with export/import.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -6,3 +6,29 @@ This is my personal website, including:
 - About me
 - Blog posts + comments
 - Projects like Animaldex, CatchEmAll
+
+## Language learner
+
+`/projects/language-learner` teaches Dutch and Korean (explained in English) and
+English (explained in Dutch), from A1 to C1. Korean starts with a Hangul level.
+It runs entirely in the browser: no database tables, migrations or API keys.
+
+- Course content lives in `src/lib/language-learner/courses/<lang>/<level>.ts` as
+  compact `target | translation | note` lines, plus markdown notes and
+  multiple-choice grammar questions (`prompt | answer | wrong; wrong | explanation`).
+  Exercises (choice, typing, sentence building, fill-in-the-blank, listening,
+  matching) are generated from that data. `content.test.ts` validates every lesson.
+- Endless drills are generated by code in `src/lib/language-learner/drills/`:
+  number words, Dutch/English clock times, de/het, plurals, Dutch and Korean
+  conjugation (a rule-based Korean conjugator handling the ㅂ/ㄷ/르/ㅅ/ㅎ
+  irregulars), Korean particles and counters, Hangul reading, English irregular
+  verbs, comparatives and a/an.
+- Challenges: a seeded daily challenge (first score of the day counts), 60-second
+  sprint, survival with three lives, mixed practice, level tests that mark a level
+  as done at 80%, and spaced-repetition reviews (simplified SM-2).
+- Audio uses the browser's speech synthesis, so listening exercises appear only
+  when the device has a voice for the language. Romanization of Korean is
+  approximate Revised Romanization.
+- Progress, streaks and settings are stored in `localStorage`
+  (`language-learner-v1`), per browser. Export/import on the overview page moves
+  them between devices.