event-model, client-core, transcript-ui: carry main's LimitReached event

The merge that brought main into rustify added Event::LimitReached to the
server's drivers, but on this branch the enum lives in event-model, which
the merge left without it, so ai-server (and ui-sandbox.sh) did not build.
Definition copied from main's driver.rs; the fold mirrors TranscriptItems.kt's
LimitNote; the iris row shows the epoch until P1 brings a time formatter.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

iris/transcript-ui/src/row.rs

@@ -60,6 +60,15 @@ fn item_content(item: &TranscriptItem) -> (Option<&str>, String) {
         TranscriptItem::PeerNote { from, text, .. } => (Some(from.as_str()), text.clone()),
         TranscriptItem::Note { text, .. } => (None, text.clone()),
         TranscriptItem::ClearedNote { .. } => (None, "_Context cleared._".to_string()),
+        // Epoch seconds as-is until the port has a relative-time formatter
+        // (P1); the Compose `LimitRow` draws it as a countdown.
+        TranscriptItem::LimitNote { resets_at, .. } => (
+            None,
+            match resets_at {
+                Some(at) => format!("_Usage limit reached; resets at {at:.0} (epoch seconds)._"),
+                None => "_Usage limit reached._".to_string(),
+            },
+        ),
         TranscriptItem::CompactedNote {
             pre_tokens,
             post_tokens,