Polish issue chat actions and overflow

- Scale activity components (events, runs) to ~80% font size with
  xs avatars for a quieter visual weight
- Hide succeeded runs from the timeline; only show failed/errored
- Always show three-dots menu on agent comments with "Copy message"
  option, plus optional "View run" when available
- User avatar repositioned to top-right (items-start) of message
- Change "Me" → "You" in assignee labels for natural chat phrasing
  ("You updated this task")

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/lib/issue-chat-messages.ts

@@ -485,6 +485,7 @@ export function buildIssueChatMessages(args: {
   }
 
   for (const run of [...linkedRuns].sort((a, b) => toTimestamp(runTimestamp(a)) - toTimestamp(runTimestamp(b)))) {
+    if (run.status === "succeeded") continue;
     orderedMessages.push({
       createdAtMs: toTimestamp(runTimestamp(run)),
       order: 2,