Sync CLAUDE.md with actual codebase

[haydenk]

CLAUDE.md was substantially out of sync with the code. A pass has been done to remove B2/Backblaze references and correct CLI flag names, but a full review is needed to verify all remaining sections are accurate:

• Verify the project structure tree matches actual files
• Verify all crate module descriptions match what exists
• Verify CLI flags for both downloader and etl match clap struct definitions
• Verify the database schema section matches actual migration files
• Verify environment variable table is complete and accurate
• Verify all mise run task names match files in .mise/tasks/

This issue should be the last closed before tagging v0.1.0 — it serves as a final accuracy check.