feat: add audio ducking settings and level control

[mdelrosario92]

Summary

• replace mute-while-recording with audio ducking toggle + level slider in settings
• add audio ducking settings/migration and apply volume ducking in recording flow
• implement cross-platform volume snapshot/restore to return to original level
• add proper translations for all 14 supported languages (cs, de, en, es, fr, it, ja, pl, pt, ru, tr, uk, vi, zh)

Testing

• cargo test (src-tauri)
• bun run lint
• bun run format:check

[cjpais]

Is this not #547?

What makes your approach better? Have you read that existing thread? You also did not provide screenshots or anything else, so I'm less favorable to this PR out of the gate. Nor did you follow the PR template.

[mdelrosario92]

Oops, you're right! I'm silly and completely missed that #547 was already covering this. My apologies for the duplication and for missing the PR template - I should have checked existing PRs first. Closing this now to avoid any further confusion!