fix(agents): chain AGENTS git hooks to global core.hooksPath

The local core.hooksPath override set by agents-init shadowed the user's
global hooks (ggshield, Git LFS) since git honors only one hooksPath. Each
shim now execs the global/system hook of the same name after running
version-bump, so global hooks still run after version increment. Bumped the
agents-tools version marker to 2 so existing AGENTS repos refresh.

scripts/agents-tools/hooks/prepare-commit-msg

@@ -1,7 +1,18 @@
 #!/usr/bin/env bash
-# agents-tools-version: 1
-# Delegates to the repo's committed .agents-tools/version-bump. Guarded so a
-# missing script or failed rev-parse never blocks the commit (always exit 0).
+# agents-tools-version: 2
+# Runs the committed .agents-tools/version-bump, then chains to the user's
+# global/system git hook (core.hooksPath) so any global prepare-commit-msg
+# still runs. agents-init's local core.hooksPath override would otherwise
+# shadow it. Guarded so a missing script or failed rev-parse never blocks the
+# commit; only the chained global hook can fail it.
 root="$(git rev-parse --show-toplevel 2>/dev/null)" || exit 0
 [ -x "$root/.agents-tools/version-bump" ] && "$root/.agents-tools/version-bump" prepmsg "$1"
+
+# Chain to the global/system hook this local override is shadowing.
+global_hooks="$(git config --global core.hooksPath 2>/dev/null)"
+[ -z "$global_hooks" ] && global_hooks="$(git config --system core.hooksPath 2>/dev/null)"
+if [ -n "$global_hooks" ]; then
+  global_hooks="${global_hooks/#\~/$HOME}" # git stores ~ verbatim
+  [ -x "$global_hooks/prepare-commit-msg" ] && exec "$global_hooks/prepare-commit-msg" "$@"
+fi
 exit 0