Complete repository health remediation

[solomonneas]

Summary

This closes the repository health audit by making the documented exporter commands work, removing third-party font requests, and adding checks for the browser code and tracked secrets.

• Support repeated Claude Code and Codex source directories, archived Codex sessions, SQLite backfill, and JSON summaries.
• Deduplicate overlapping sources and calculate source counts after date filtering.
• Share session view-model logic across all five page variants.
• Run Python, frontend syntax, frontend behavior, and secret checks in GitHub Actions and the pre-push hook.
• Update installation, development, privacy, and changelog documentation.

Verification

• python3 -m pytest tests/ -q (39 passed)
• python3 -m compileall -q bin scripts tests
• python3 scripts/check_frontend.py index.html
• node tests/frontend.test.js
• python3 scripts/scan_repo.py .
• Browser check: HTTP 200, all five variants rendered, no external requests or console errors with generated usage data.

Review notes

The exporter backfill uses Codex SQLite totals only when rollout usage for that thread is missing. Those records keep cost unknown because the database does not contain the per-call token breakdown needed for an accurate estimate.