feat: Add ASYNC_CORRECTION support for dictate-ws (API-431)

[hilnius]

Summary

• Opt into enable_async_corrections on the dictate-ws CONFIG frame and add the AsyncCorrection server message type.
• Handle ASYNC_CORRECTION in the dictate page by replacing the trailing suffix of the note with replacement.
• Bump API_VERSION to 2026-07-01 in both frontend and backend.

Closes API-431.

Test plan

• Open the Dictate page and start a session — confirm CONFIG includes "enable_async_corrections": true in the WS log.
• Dictate a phrase that triggers a correction — DICTATED_TEXT segments append, then ASYNC_CORRECTION updates the trailing note text in place.
• Pause, clear, and resume dictation — existing flows still work.
• CI passes (tsc + vite build).

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