feat(v0.2): tab status dot, activity (unread) indicator, drag-reorder

- terminal-session.ts: track SessionStatus (connecting/connected/reconnecting/
  exited) + onStatus callback; FIX: wire onTitleChange (onTitle was in opts but
  never bound — auto-title was dead)
- tabs.ts: per-tab status dot (color = connection state), unread flag set on
  background output + cleared on activate, HTML5 drag-to-reorder (preserves
  active tab, persisted)
- style.css: .tab-dot colors, .unread ring, .dragging/.drag-over feedback
- Browser-verified: green dot connected, unread ring after bg output, reorder
  AAA|BBB→BBB|AAA persists across reload. 191 tests green, typechecks + build ok.

public/style.css

@@ -62,6 +62,43 @@ html, body {
   box-shadow: inset 0 -2px 0 #4a9eff; /* active underline accent */
 }
 
+/* Status dot — color reflects connection state. */
+.tab-dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+  margin-right: 8px;
+  flex: none;
+  background-color: #666;
+}
+.dot-connected {
+  background-color: #3fb950; /* green */
+}
+.dot-connecting,
+.dot-reconnecting {
+  background-color: #d29922; /* amber */
+}
+.dot-exited {
+  background-color: #f85149; /* red */
+}
+
+/* Unread: an inactive tab got new output — blue ring + brighter label. */
+.tab.unread .tab-dot {
+  box-shadow: 0 0 0 2px rgba(74, 158, 255, 0.6);
+}
+.tab.unread .tab-label {
+  color: #fff;
+  font-weight: 600;
+}
+
+/* Drag-to-reorder feedback. */
+.tab.dragging {
+  opacity: 0.4;
+}
+.tab.drag-over {
+  box-shadow: inset 3px 0 0 #4a9eff; /* drop-position indicator */
+}
+
 .tab-label {
   padding-right: 8px;
   overflow: hidden;