feat(hooks): ring terminal on turn end via Stop hook

Notification matcher covers input-needed events only; end of turn had no
signal but idle_prompt, ~60s late. Wire notify-attention.sh on Stop too,
branching on hook_event_name for the message. Signal only: returns
terminalSequence + suppressOutput, never blocks (guard vs BDR-083).

Header documents both client-side prerequisites found in BLK-020.

settings.json

@@ -286,6 +286,18 @@
         ]
       }
     ],
+    "Stop": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "bash ~/.claude/hooks/notify-attention.sh",
+            "timeout": 5,
+            "statusMessage": "Ringing terminal bell..."
+          }
+        ]
+      }
+    ],
     "UserPromptSubmit": [
       {
         "hooks": [