UI: mobile responsive layout, streamline agent budget display, and xs avatar size

Make agents list force list view on mobile with condensed trailing
info. Add mobile bottom bar for config save/cancel and live run
indicator on agent detail. Make MetricCard, PageTabBar, Dashboard
tasks, and ActivityRow responsive for small screens. Add xs avatar
size for inline text flow. Remove redundant budget displays from
agent overview, properties panel, costs tab, and config form.
Add attachment activity verb labels.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/pages/IssueDetail.tsx

@@ -31,6 +31,8 @@ const ACTION_LABELS: Record<string, string> = {
   "issue.checked_out": "checked out the issue",
   "issue.released": "released the issue",
   "issue.comment_added": "added a comment",
+  "issue.attachment_added": "added an attachment",
+  "issue.attachment_removed": "removed an attachment",
   "issue.deleted": "deleted the issue",
   "agent.created": "created an agent",
   "agent.updated": "updated the agent",