Fix token_count discovery for updated Codex sessions

[k-shimura7617]

Summary

Fix token_count discovery when Codex continues writing to a session file under an older date directory.

Root Cause

The extension's fallback search only checked date directories from the previous seven calendar days. Codex can keep appending new events to an older session file, so a file can have a current mtime while its path date remains older than seven days.

When that happens, the extension skips the active session file and shows:

No token_count events found in session files

Changes

• Build session search roots from the configured session path.
• Recursively search rollout-*.jsonl under those roots.
• Sort discovered files by mtime so recently updated sessions are checked first.
• Include ~/.codex/archived_sessions for the default Codex session path.
• Keep the existing fast path for today's recently modified session files.

Validation

• Reproduced locally with a fixture where token_count exists under an older date directory while the file mtime is current.
• Confirmed the old implementation returns No token_count events found in session files.
• Confirmed the patched implementation discovers the same fixture file.
• Ran npm run compile.