[Bug]: AI activity log timestamps are shown in UTC instead of local time

[ymadd]

Describe the bug

Timestamps in the AI Activity log (Settings → AI Activity) are rendered in UTC rather than the user's local time. The Events table, the Sessions list/cards, the event detail modal, and the CSV/JSON exports all show the raw backend timestamp (chrono::Utc::now().to_rfc3339()), so a user in UTC+9 sees an event that happened at 19:00 local displayed as 10:00.

The display code sliced the ISO string directly (ev.timestamp.replace("T", " ").slice(0, 19)) instead of converting to local time, and the Rust CSV/JSON/notebook exporters wrote the UTC value verbatim.

To Reproduce

1. Enable AI/MCP with the audit log (Settings → AI).
2. Run a few MCP tool calls so events are recorded.
3. Open Settings → AI Activity → Events.
4. Compare a timestamp with your wall-clock time — it is shown in UTC, not local.
5. Export to CSV/JSON — the exported timestamps are UTC as well.

OS Version

macOS (Darwin 25.5.0)

Tabularis Version

v0.11.0

Relevant Log Output

(n/a — display/formatting issue)