fix(indexer): streaming reads, per-file transactions, and error reporting

- Replace readFileSync+split with chunked line reader (readLines) to
    avoid loading entire JSONL files into memory at once
  - Wrap each file's indexing in its own transaction so one corrupt file
    doesn't roll back the entire index
  - Log warnings to stderr instead of silently swallowing errors in
    indexSubagentMeta, indexWorkflows, and indexHistory
  - Add try/catch around readdirSync calls in discoverJsonlFiles and
    indexWorkflows to survive unreadable directories
  - Push error-pattern filtering in failures() into SQL LIKE clauses
    instead of scanning all tool_results in JS

.gitignore

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+.DS_Store