fix: embed pre-commit error details into block reason field

Claude Code hook system only shows the JSON reason field to the agent,
stderr output is invisible. Move detailed error info from stderr into
the reason so the agent can see exactly what failed and fix it directly.

Author: majiayu000

hooks/pre-bash-guard.sh

@@ -109,11 +109,13 @@ if echo "$COMMAND_STRIPPED" | grep -qE 'git\s+commit\b'; then
       PRECOMMIT_OUTPUT=$(VIBEGUARD_DIR="${VIBEGUARD_DIR:-$(cd "$HOOK_DIR/.." && pwd)}" bash "$PRECOMMIT_SCRIPT" 2>&1) || PRECOMMIT_EXIT=$?
       if [[ $PRECOMMIT_EXIT -ne 0 ]]; then
         vg_log "pre-bash-guard" "Bash" "block" "pre-commit check failed" "$COMMAND"
-        echo "$PRECOMMIT_OUTPUT" >&2
+        # Embed detailed output into reason so Claude Code can see it
+        # (stderr is not visible to the agent, only the JSON reason field is)
+        ESCAPED_OUTPUT=$(printf '%s' "$PRECOMMIT_OUTPUT" | python3 -c 'import sys,json; print(json.dumps(sys.stdin.read())[1:-1])')
         cat <<BLOCK_EOF
 {
   "decision": "block",
-  "reason": "VIBEGUARD Pre-Commit check failed. Please fix the problem according to the error message above and resubmit. The use of environment variables to bypass is prohibited."
+  "reason": "VIBEGUARD Pre-Commit 检查失败。请根据上方错误信息修复问题后重新提交。禁止使用环境变量绕过。\n\n${ESCAPED_OUTPUT}"
 }
 BLOCK_EOF
         exit 0