Fix M4 reactivity bugs: active border, Ctrl+K, diagnostics

- Drill activeLeafId as a separate prop through Pane -> SplitNode ->
  LeafPane instead of bundling it into the \$derived ops object.
  Passing activeLeafId via ops caused subsequent focus changes to
  not propagate to children (LeafPane's active = \$derived(...) wasn't
  re-evaluating when ops's identity changed). Drilling sidesteps any
  prop-as-derived-object reactivity quirks.
- Ctrl+K listener now uses capture phase so it wins over xterm.js's
  keydown handler inside the focused terminal.
- Bump active/broadcasting borders to 2px and brighter colors so the
  visual change is unmissable.
- Add a 🔔 test-toast button in the titlebar to verify the
  notification pipeline independently of idle detection.
- Sprinkle console.log diagnostics through the active/broadcast/
  idle/notify flows so we can pinpoint any remaining issues from
  devtools next time something looks off.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/layout/LeafPane.svelte

@@ -7,12 +7,14 @@
   let {
     leaf,
     ops,
+    activeLeafId,
   }: {
     leaf: LeafNode;
     ops: PaneOps;
+    activeLeafId: string | null;
   } = $props();
 
-  const active = $derived(ops.activeLeafId === leaf.id);
+  const active = $derived(activeLeafId === leaf.id);
 
   let status = $state("starting…");
   let statusOk = $state(true);
@@ -82,9 +84,11 @@
 
   function checkIdle() {
     if (notifiedThisIdle) return;
-    if (Date.now() - lastDataTime >= IDLE_THRESHOLD_MS) {
+    const sinceLast = Date.now() - lastDataTime;
+    if (sinceLast >= IDLE_THRESHOLD_MS) {
       notifiedThisIdle = true;
       const name = leaf.label ?? leaf.distro ?? "pane";
+      console.log("[tiletopia] notifying idle:", leaf.id, "quietForMs:", sinceLast);
       ops.notify(`${name} is idle`);
     }
   }
@@ -96,7 +100,10 @@
 
   // ---- broadcast -----------------------------------------------------------
   function onTerminalInput(b64: string) {
-    if (leaf.broadcast) ops.broadcastFrom(leaf.id, b64);
+    if (leaf.broadcast) {
+      console.log("[tiletopia] broadcasting from:", leaf.id);
+      ops.broadcastFrom(leaf.id, b64);
+    }
   }
 
   // ---- focus / active ------------------------------------------------------
@@ -107,6 +114,7 @@
   });
 
   function onPaneClick() {
+    console.log("[tiletopia] pane click:", leaf.id, "currentlyActive:", active);
     if (!active) ops.setActivePane(leaf.id);
   }
 
@@ -232,14 +240,17 @@
     border: 1px solid transparent;
     box-sizing: border-box;
   }
+  .leaf {
+    border-width: 2px;
+  }
   .leaf.active {
-    border-color: #3a5a8c;
+    border-color: #5a8cd8;
   }
   .leaf.broadcasting {
-    border-color: #c98a1f;
+    border-color: #e09838;
   }
   .leaf.active.broadcasting {
-    border-color: #e0a432;
+    border-color: #ffb840;
   }
 
   .pane-toolbar {