feat(server): dictionaries, loaded from files and searched

The server now holds dictionaries for everyone: `dictionary_entry` and
`dictionary_source`, reference data owned by no one, never synced. It
loads the dictionary files in its `dictionaries` folder at every start,
those whose SHA-256 changed: in the background, each source replaced in
one transaction, so searches meanwhile find the old entries; a file it
can't read is logged and left out. All of JMdict loads in under half a
minute. On an instance the folder is deploy/dictionaries, mounted
read-only (compose.yaml); the server's README says how.

DictionaryEndpoint (signed in): the dictionaries with their credits; a
search (exact key, exact loose key, key starting with the query, loose
key starting with it, each in the source's order; katakana as hiragana,
macrons written out), some 150-450 ms over all of JMdict; and the
entries with a label, counted and a page at a time (all JLPT N5 words).

The curator now keeps spellings that aren't quite right apart, as
`looseKeys` (romaji with long vowels typed once): "sushi" finds 寿司
before 数詞 (すうし).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_curator/README.md

@@ -51,6 +51,7 @@ The **first line** says what the file holds:
 | `labels` | What it can be picked by: `common`, `jlpt:n5` … `jlpt:n1` (later e.g. `hsk:3`, `topik:1`). |
 | `rank` | Its order among the source's entries, lower first; JMdict: N5 to N1 in their lists' order, then other common words, then the rest. |
 | `keys` | What a search matches, lower case: written forms, readings in their own script and romanised, meanings. Everything specific to a language happens here, so the server's search knows no language. |
+| `looseKeys` | What a search matches after every `keys` match: spellings people type that aren't quite right (romaji with long vowels typed once, `sushi` for すうし). Left out when empty. |
 | `entry` | The entry itself, as cards take it: `forms` and `readings` (`text`, `common`, the source's `tags`; for a reading the `forms` it belongs to), `senses` (`glosses`; the source's codes in `pos`, `misc`, `field`, `dialect`; `info`; the `forms` and `readings` a sense is limited to). Lists are left out when empty. |
 
 ## Adding a source