style: align trigger timestamp with simulation Cost line typography

The "May 3, 2026 at 4:53 AM UTC" timestamp in email's "What Triggered
This Workflow" section was indented under the trigger description and
used a smaller (14px) non-italic font, while the simulation Cost
placeholder ("⛽ (cost shown at the Deploy step)") sits at the
left margin in italic gray. Visually inconsistent for two pieces of
secondary metadata.

Match the typography: drop the 18px left indent, switch to 20px top
margin (matches the gap between section divs), drop the font-size
override, add font-style: italic. Both lines now share the same
italic-gray treatment.

Author: will-dz

core/taskengine/summarizer_format_email.go

@@ -266,7 +266,10 @@ func buildAnalysisHtmlFromStructured(s Summary) string {
 		// Add timestamp row if available
 		if s.TriggeredAt != "" {
 			if ts := formatTimestampHumanReadable(s.TriggeredAt); ts != "" {
-				sb.WriteString("<p style=\"margin: 4px 0 0 18px; color: #666; font-size: 14px;\">")
+				// Same typographic treatment as the simulation Cost placeholder line
+				// (italic, gray, no left indent) — secondary metadata that visually
+				// flanks the primary content.
+				sb.WriteString("<p style=\"margin: 20px 0 0 0; color: #666; font-style: italic;\">")
 				sb.WriteString(html.EscapeString(ts))
 				sb.WriteString("</p>")
 			}