feat(frontend): add Created on timestamp to conversation overview

[dembrane-sam-bot]

This PR adds the conversation creation timestamp (Created on) to the conversation overview tab, directly under the title and in the same row as the tags. This matches the list page's display and avoids portraying the timestamp as the exact 'recording started' time (which can diverge if a participant sits on the mic-permission screen).

[spashii]

Holding until after the release, and one real problem to fix first: this reads created_at, which is when the conversation row was created, not when recording started. A participant who scans the QR and sits on the mic-permission screen for ten minutes gets a 'recording started' time that is ten minutes early. Either derive the value from the telemetry recording_started_at (the monitor drilldown timeline already uses it) or relabel the field to 'Created on' so it says what it shows.

[dembrane-sam-bot]

You're 100% right. created_at represents when the conversation row was created (e.g., when the QR code was scanned), not when recording actually started. Since recording_started_at is transient telemetry in Redis that isn't persisted in Postgres for historical/completed conversations, keeping the UI label as Created on is the correct way to accurately show what the timestamp represents.

I have updated the PR title and description to align with 'Created on' rather than 'Recording started' to make this clear. Ready for your review whenever the release is out!