feat: add rich run timeline UI with collapsible cards and jump-to-message

- Add RunTimeline component with vertical event timeline, collapsible run
  cards, per-kind icons, status animations, and agent lane badges
- Add runTimelineFormatting helpers for timestamps, durations, labels,
  content truncation, and consecutive thinking-event collapsing
- Integrate Timeline section into ActivityPanel between Agents and Tools
- Wire jump-to-message in App.tsx using DOM data-message-id attributes
  on ChatPane messages with smooth scroll and temporary highlight ring
- Add comprehensive unit tests for all formatting helpers
- Update HANDOVER.md to document completed frontend implementation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/components/ChatPane.tsx

@@ -391,7 +391,7 @@ export function ChatPane({
                   phase === 'thinking' ? 'Thinking' : phase === 'final' ? 'Final' : undefined;
 
                 return (
-                  <div className="group py-3" key={message.id}>
+                  <div className="group py-3" data-message-id={message.id} key={message.id}>
                     <div className="flex gap-3">
                       <div
                         className={`mt-0.5 flex size-7 shrink-0 items-center justify-center rounded-full ${