feat(#1290): show per-agent loose-end question count in dashboard

Add a '❓ N' badge to each container row showing the count of pending
questions where the agent is the asker (awaiting an answer) or the
target (owes a reply). Derived live from questionsState — no backend
field needed.

Details:
- New .badge-loose-ends CSS class (purple, matching Q33R1ES section colour)
- Badge tooltip breaks down the count: 'N asked, N to answer'
- renderContainersFromState() called on QuestionAdded/QuestionResolved
  so the badge updates instantly when question state changes
- Existing ⏰ reminders badge kept separate (different signal)

frontend/packages/dashboard/src/common.css

@@ -78,6 +78,10 @@ code {
   color: var(--cyan); border-color: var(--cyan);
   text-shadow: 0 0 6px rgba(137, 220, 235, 0.4);
 }
+.badge-loose-ends {
+  color: var(--purple); border-color: var(--purple);
+  text-shadow: 0 0 6px rgba(203, 166, 247, 0.4);
+}
 /* Context-window usage badges on dashboard container rows. */
 .badge-ctx-ok {
   color: var(--green); border-color: var(--green);