Audio recording custom property and email thread UI

Two quality-of-life features that came out of real usage patterns: recruiters wanted to record quick voice notes after phone screens, and the email view needed better thread context.

Audio recording

A new custom property type: audio. Record directly in the browser and attach the recording to a candidate's profile. Play it back later from the candidate detail page with a built-in audio player. Useful for capturing tone, enthusiasm, and the nuances that don't translate to text notes.

Email thread UI

Email conversations now display full thread metadata: who replied, when, and the thread hierarchy. Merge field processing was also refactored to handle more complex template variables reliably, so your automated emails render candidate and position data correctly every time.