chore: Halkyon Learn moves into apps/learn

Its server, client, app and curator, and the tools that write its
assets (maps, Anki fixtures, icons), as they are; paths are fixed in
the commits that follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/halkyon_learn_curator/data/README.md

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+# Data the curator brings along
+
+What the dictionaries draw on besides their sources, and never changes, so
+`curate update` needs only EDRDG's files of the day, MDBG's CC-CEDICT and
+Wiktionary's dump.
+
+`jlpt/n1.csv` … `n5.csv` are the JLPT vocabulary lists of
+[yomitan-jlpt-vocab](https://github.com/stephenmk/yomitan-jlpt-vocab)
+(`original_data`, as of 2026-10-09), CC BY-SA 4.0 (`jlpt/LICENSE.txt`): Jonathan
+Waller's lists ([tanos.co.uk](http://www.tanos.co.uk/jlpt/), CC BY) with each
+word's JMdict entry and its most common spelling, by stephenmk.
+
+`kanji-jlpt.json` maps each kanji on Jonathan Waller's JLPT kanji lists
+([tanos.co.uk](http://www.tanos.co.uk/jlpt/), CC BY) to its level, 5 for N5 to 1
+for N1: the `jlpt_new` of
+[kanji-data](https://github.com/davidluzgouveia/kanji-data)'s `kanji.json`
+(MIT, as of 2026-10-09), nothing else of it.
+
+The lists are over ten years old and won't change; replace them only for a list
+of the same shape.
+
+`wordfreq/small_<language>.msgpack.gz` are wordfreq's lists of how often words
+are used ([wordfreq](https://github.com/rspeer/wordfreq) v3.0, as of 2021-03-29,
+the last change to its data), unchanged: CC BY-SA 4.0, by Robyn Speer, drawn from
+SUBTLEX (Marc Brysbaert et al., whose authors wordfreq's licence asks to be
+credited, and who made SUBTLEX freely available), OpenSubtitles, Wikipedia,
+Google Books Ngrams and others, as wordfreq's README lists them. The Wiktionary
+dictionaries take their ranks and their `common` label from them and credit
+both. wordfreq's data won't change: it was sunset in 2024.
+
+`hsk/syllabus2025_words.tsv` lists the 10,896 words of the HSK examination
+syllabus published in November 2025 by the Center for Language Education and
+Cooperation (中外语言交流合作中心), the one HSK 3.0's examination follows since
+July 2026, each with its level (1 to 6, 7 for 7 to 9), the level of a homograph
+graded twice, its pinyin and its part of speech: as extracted from the
+syllabus's PDF by Alvaro Serrano's [hsk30](https://github.com/harukicoder/hsk30)
+(`corpus/syllabus2025/`, as of 2026-09-06), MIT (`hsk/LICENSE.txt`), unchanged.
+Only each word's level reaches the dictionaries (`hsk:N`), with the pinyin to
+tell CC-CEDICT's readings of one word apart; the curator credits both. The
+Ministry claims copyright on the standard's documents; a word's level is a fact
+about it, which the dictionaries keep with attribution (decided 2026-10-14).
+`hsk/syllabus2025_chars.tsv` lists the syllabus's 3,088 characters to recognise
+(认读字) with their levels (246, 125, 284, 441, 431 and 413 for levels 1 to 6,
+1,148 for 7 to 9), from the same repository and commit (`corpus/syllabus2025/`),
+MIT, unchanged; they label the Chinese characters (`hsk:N`) as the words' label
+the words.