fix(failures): use is_error field instead of content pattern matching

Index the is_error boolean from JSONL tool_result blocks into a new
  column, replacing the old ERROR_PATS text-matching approach that
  produced ~90% false positives. Bash exit code pattern kept as fallback.

.gitignore

@@ -1 +1,2 @@
-.DS_Store
+.DS_Store
+plans/