audio: CrisperWhisper long-form overlap windowing (no seam drops)

Contiguous windows dropped words at each ~28s seam (Whisper's weak edge context +
words straddling the boundary). Now use overlapping windows (29s wide, 24s hop =
5s overlap), advancing by the hop and transcribing each full window, then
de-duplicate the overlap by keeping only words that start at/after the last kept
word's end, and rebuild the transcript from the de-duped words. Verified on an
~11min clip: 0 gaps >2s across all seams, continuous word timestamps to 673s,
recovered the previously-dropped seam words.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R6iugoNeEgt9PkajKrFyq4