feat: 1.2.0 practice window + quality close-out - #232

Scopes practice down to a question bank from full entries only, local judging with the corpus
explanation on a miss, and a bounded local progress file that is data rather than configuration. It
offers three exercise shapes, does not touch the candidate window, stores nothing remotely and keeps
the learning resource on demand, with acceptance criteria that include only full entries and no
change to the latency or memory gates.

Signed-off-by: wangzhizhou <824219521@qq.com>

…n codes

Practice is limited to entries the corpus marks as full, so the app never tests the user on data it is
itself unsure about. Two exercise shapes: typing a character's full code, and choosing the last stroke
and structure to derive the recognition letter, with the reverse table shared with the corpus rules.

Progress lives in practice.tsv under application support as data rather than configuration, bounded to
three thousand rows and 256 KiB, written atomically and reset by deletion. The window is independent
and non-modal, opened by a new alt+k chord that joins the existing hotkey schema, so it appears in the
settings list with the same collision checks.

Signed-off-by: wangzhizhou <824219521@qq.com>

Cold first key measures about twenty eight milliseconds with the learning area off, so it is not caused
by the panel and the user reports no perceptible pause; it stays disclosed separately as before.
Ranking observation, fixed order, level three codes, cold key optimisation and pinyin backend work are
all closed for this release with explicit conditions that would reopen them, so nothing remains
vaguely pending. The report also records which memory number is authoritative.

Signed-off-by: wangzhizhou <824219521@qq.com>