Wrap stop hook lgtm output

- Keep Stop hook stdout valid JSON so Codex can parse it.
- Move `./bin/brew lgtm` handling into a wrapper script.

.codex/hooks.json

@@ -5,7 +5,7 @@
         "hooks": [
           {
             "type": "command",
-            "command": "./bin/brew lgtm >&2 && printf '{\"continue\":true}'",
+            "command": ".codex/hooks/brew-lgtm-stop.sh",
             "timeout": 360
           }
         ]

.codex/hooks/brew-lgtm-stop.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+cd "$(dirname "$0")/../.." || {
+  printf '%s\n' '{"decision":"block","reason":"Failed to cd to the repository root before running ./bin/brew lgtm."}'
+  exit 0
+}
+
+if ./bin/brew lgtm >&2
+then
+  printf '%s\n' '{"continue":true}'
+else
+  printf '%s\n' '{"decision":"block","reason":"./bin/brew lgtm failed; review the output above and fix it before stopping."}'
+fi