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/test/fixtures/makemeahanzi-dictionary-sample.txt

@@ -0,0 +1,2 @@
+{"character":"水","definition":"water, liquid, lotion, juice","pinyin":["shuǐ"],"decomposition":"⿻亅？","etymology":{"type":"pictographic","hint":"A river running between two banks; compare 川"},"radical":"水","matches":[[0],null,null,null]}
+{"character":"海","definition":"sea, ocean; maritime","pinyin":["hǎi"],"decomposition":"⿰氵每","etymology":{"type":"pictophonetic","phonetic":"每","semantic":"氵","hint":"water"},"radical":"氵","matches":[[0],[0],[0],[1],[1],[1],[1],[1],[1],[1]]}