Tolerate missing terminal punctuation in dictée answers

Manual test: the Piper voice (previous commit) is now intelligible,
but typing exactly what's heard ("Les petits chats dorment", no
period) was rejected. The provisional audio never vocalizes
punctuation, so nothing tells the child to add it — penalizing its
absence punishes information they were never given.

DictationAnalyzer now strips terminal punctuation (. ! ? …) from both
sides before comparing, in the exact-match/variant check and before
word alignment, without touching punctuation elsewhere in the
sentence. A real error on the last word is still caught (added test).

A scene-level test reproducing the exact reported interaction
(tests/exercises/test_exercise_host_dictation.gd) failed before the
fix and passes after.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/exercises/test_exercise_host_dictation.gd.uid

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+uid://dcas0r0cf6k7u