Crash: ENOENT on project dirs containing subagent directories

[AgentSeal]

Some project directories under ~/.claude/projects/ contain subagent directories (UUIDs like 68b2ace0-...) with no matching .jsonl file.

CodeBurn crashes with ENOENT when it encounters these.

The parser should skip directories and non-session entries gracefully instead of assuming every entry in a project dir has a readable .jsonl sibling.

[AgentSeal]

Fixed in 3964478. parseSessionFile now catches read errors and skips the file.