fix(autopilot): use readable UTC timestamp in issue description

Autopilot was formatting the triggered-at timestamp with time.RFC3339
(e.g. "2026-04-16T14:54:32Z"), which is hard to read and confusing for
users in non-UTC timezones because the "Z" suffix looks like an error
instead of a timezone indicator.

Switch to a human-readable format ("2026-04-16 14:54 UTC") so only the
hour differs from local time; minutes match across timezones, making
the value easy to reconcile at a glance.

Fixes multica-ai/multica#1197.

server/internal/service/autopilot.go

@@ -321,7 +321,7 @@ func (s *AutopilotService) publishRunDone(workspaceID string, run db.AutopilotRu
 // user-provided description, asking the agent to rename the issue after
 // it understands the actual work.
 func (s *AutopilotService) buildIssueDescription(ap db.Autopilot) pgtype.Text {
-	now := time.Now().UTC().Format(time.RFC3339)
+	now := time.Now().UTC().Format("2006-01-02 15:04 UTC")
 	note := fmt.Sprintf("\n\n---\n*Autopilot run triggered at %s. After starting work, rename this issue to accurately reflect what you are doing.*", now)
 	base := ap.Description.String
 	return pgtype.Text{String: base + note, Valid: true}