feat: add crates/transcript with TranscriptAccumulator

[devin-ai-integration]

feat: add crates/transcript with TranscriptAccumulator

Summary

Extracts the TranscriptAccumulator into a new standalone crates/transcript shared crate — the crate-only portion of #4064, with no plugin or desktop app integration.

The accumulator processes streaming ASR StreamResponses into clean, deduplicated transcript words using a two-level design:

• Within a response: assemble aligns tokens to the transcript string (sole oracle for word boundaries — no timing heuristics)
• Across responses: stitch uses a 300ms timing heuristic to merge words split across final responses (e.g. Korean particles)

Per-channel state handles watermark-based dedup, partial word splicing, and held-word stitching. 37 unit tests pass, including fixture replay tests against real Deepgram and Soniox data (English + Korean).

Nothing depends on this crate yet — integration into plugin-listener/plugin-listener2 is a follow-up.

Review & Testing Checklist for Human

• Verify spacing_from_transcript greedy-forward find handles repeated substrings in transcripts correctly (e.g. "the the") — mismatch could silently assign wrong spacing
• Review the 300ms threshold in should_stitch — this is the heuristic for merging words split across responses; confirm it works for your provider mix
• Confirm splice boundary conditions (<= / >=) don't drop or duplicate words at exact timestamp boundaries
• Run cargo test -p transcript locally to confirm fixture tests pass against current hypr-data

Notes

• Files were extracted directly from the refactor/transcript-accumulator-to-shared-crate branch (PR refactor: move TranscriptAccumulator to shared crate, migrate batch streaming path #4064) via git checkout
• Uses edition = "2024" — matches the convention on that branch
• Link to Devin run
• Requested by @yujonglee

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR that start with 'DevinAI' or '@devin'.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[netlify]

✅ Deploy Preview for hyprnote-storybook canceled.

Name	Link
🔨 Latest commit	e7eb1ce
🔍 Latest deploy log	https://app.netlify.com/projects/hyprnote-storybook/deploys/6997c9369d5e4d0008d7ed21

[netlify]

✅ Deploy Preview for hyprnote canceled.

Name	Link
🔨 Latest commit	e7eb1ce
🔍 Latest deploy log	https://app.netlify.com/projects/hyprnote/deploys/6997c93673135a0008b34c8d