feat(app): write kanji, kana and words by hand, each stroke checked

The study option Write by hand (settings schema 7) has character cards
and words written in a session, on a schedule of their own (review mode
`write`; older apps skip a mode they don't know): what to write on top, a
character's meanings and readings or a word's reading and meanings, and
below it a square to write it in, character by character.

Each stroke is checked as it ends against KanjiVG's: both resampled to 22
points, then their shape once centred, where they lie, how long they are
and which way they go, each against what a loose hand strays by; a stroke
closer to one still to come is out of order. One that counts is drawn as
KanjiVG draws it, and the hand's offset from the middle is forgiven in the
strokes after; any other flashes red, says why and counts as a mistake, as
does a hint. Two misses in a row show the next stroke faintly. Once
written, or given up on (Show it), the rating the mistakes suggest is
outlined: none Good, one or two OK, more Bad.

The square takes every touch on it at once, so writing never scrolls the
card or swipes to rate. Characters without a stroke order (in a word) are
written for the person.

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>

docs/adr/0004-tree-tags-review-modes-settings-assets.md

@@ -61,7 +61,9 @@ revision's payload, and the per-side merge of ADR 0003 becomes per field.
    heatmap, and never moves a schedule). A card's schedule replays only the reviews of
    one mode. Existing reviews are `review`. Resetting a card's progress (added
    2026-10-01) appends a `reset` entry rather than deleting reviews: schedules replay
-   only what follows it, and the streak and the heatmap keep the history.
+   only what follows it, and the streak and the heatmap keep the history. Writing a
+   character or a word by hand (added 2026-10-09) is `write`, with a schedule of its
+   own: recalling a kanji and writing it are learnt apart, as a reverse card is.
 4. **A person's settings are one synced row.** `person_settings` holds settings in a
    versioned payload: study goals now, other preferences later. Two devices creating it
    while offline make two rows; the app keeps the one with the smallest id and folds the