refactor: codebase organization audit

[nigel-hall-codes]

Audit the repo's organization and produce a migration plan. Give Fable the repo and ask it to produce:

• Current file/module map — what exists and where
• Pipeline stages — what each stage does
• Mixed responsibilities — where concerns are tangled together
• Proposed folder structure — target organization
• Migration plan — sequenced as small, reviewable PRs
• "Do not break behavior" test plan — how to verify each migration step preserves behavior

Deliverable is the audit + plan artifact. Actual reorganization happens in follow-up PRs driven by the migration plan.