ja: mark the reviewed navigation strings as verified

[yasumorishima]

navigate.yaml still had twenty-three Japanese strings sitting under lowercase t:. Per PythonScripts/audit_translations/README.md, lowercase means untranslated or unverified and uppercase means translated and verified, so promoting them is a claim about the reading rather than bookkeeping. Each line was read against the value the English source carries in the same rule — the value, not the phrase(...) hint, since those two can disagree: move-cell-next says "no next column" under a hint that reads 'no next row', and the Japanese follows the value.

Nineteen lines were already right and only change case. Four were the odd one out among their own siblings and are reworded as well. There is no Japanese appendix for navigation wording — unlike the ClearSpeak terms — so those four are a judgement call, and each one has a test:

line	was	now	why
say-command	最初の文字にズームイン	最初の文字までズームしました	the other two zoom reports in that same test are sentences (ズームインを最大にしました, 文字までズームしました); this one was a bare noun phrase and did not read as a report of where the zoom ended up
default-read-cell	現在のエントリを読む	現在のセルを読む	エントリ appears exactly once in the whole Japanese rule set; the rule speaks 行 and 列 straight after it and the sibling rule says 表, so セル is the word these rules already use
toggle-mode-up / toggle-mode-down	シンプル	簡易	the three modes are spoken as <word> + モード, and 文字 and 拡張 are ordinary words while this one was a transliteration between them
toggle-speech-describe	移動後の式の概要	移動後に式の概要を読み上げる	the two states of one toggle: the other is the sentence 移動後に式を読み上げる, and this one did not say what would happen to it

Measurements

audit-translations ja, against this branch's merge base:

	before	after
untranslated text	3415	3392
rule differences	30	30
missing / extra rules	0 / 0	0 / 0
missing / mismatched / extra definitions	0 / 0 / 0	0 / 0 / 0

The drop is exactly the number of lines promoted, and nothing structural moved.

Tests

Four in tests/Languages/ja/navigate.rs, one per reworded string. Reaching the first-character branch needs Character mode, so the helpers grew a mode argument; the command sequence is the one move_inside_leaves in src/navigate.rs uses — ZoomInAll to the leaf, then one more ZoomIn to step inside it.

To check that the tests hold the wording rather than merely passing, I pushed a branch that reverts those four readings and nothing else: exactly those four went red.