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/assignees.test.ts

@@ -47,7 +47,7 @@ describe("assignee selection helpers", () => {
   });
 
   it("formats current and board user labels consistently", () => {
-    expect(formatAssigneeUserLabel("user-1", "user-1")).toBe("Me");
+    expect(formatAssigneeUserLabel("user-1", "user-1")).toBe("You");
     expect(formatAssigneeUserLabel("local-board", "someone-else")).toBe("Board");
     expect(formatAssigneeUserLabel("user-abcdef", "someone-else")).toBe("user-");
   });

ui/src/lib/assignees.ts

@@ -76,7 +76,7 @@ export function formatAssigneeUserLabel(
   currentUserId: string | null | undefined,
 ): string | null {
   if (!userId) return null;
-  if (currentUserId && userId === currentUserId) return "Me";
+  if (currentUserId && userId === currentUserId) return "You";
   if (userId === "local-board") return "Board";
   return userId.slice(0, 5);
 }

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,