claude: Add attention-bell hook so tmux flags Claude sessions needing input

Wire Stop and Notification hooks in ~/.claude/settings.json to a new
~/.claude/hooks/attention-bell.sh, which rings the terminal bell in the
session pane so tmux monitor-bell flags the background window.

The hook runs detached (no controlling tty), so it walks its process
ancestry to the claude process and writes the BEL to that pane tty.

Also replaces the dead settings.json symlink (pointed at a now-missing
~/wrk/claude path) with a real tracked file.

.claude/settings.json

@@ -1 +0,0 @@
-/home/alexion/wrk/claude/settings.json

.claude/settings.json

@@ -0,0 +1,18 @@
+{
+  "hooks": {
+    "Stop": [
+      {
+        "hooks": [
+          { "type": "command", "command": "~/.claude/hooks/attention-bell.sh" }
+        ]
+      }
+    ],
+    "Notification": [
+      {
+        "hooks": [
+          { "type": "command", "command": "~/.claude/hooks/attention-bell.sh" }
+        ]
+      }
+    ]
+  }
+}