Store transcript history locally

[none23]

Summary

Save each successful transcription to a private on-device SQLite database. The history keeps both the raw speech-to-text output and the final text, along with the configured cleanup model and the processing path that produced the result.

Changes

• Add a typed BAML transcript record and a native Rust persistence callback.
• Store UTC timestamps, raw and final text, optional model names, and typed processing outcomes.
• Keep persistence best effort and run it after clipboard or focused-window delivery.
• Restrict the data directory and database to the current user, and reject symbolic-link database targets.
• Use the BAML 0.17 runtime model directly when deciding whether cleanup should run.
• Document the database location and plaintext storage behavior.