Docs truth pass: fix Stripe/Mollie drift, ports, branding; archive stale docs

Commit notes

- AGENTS.md: payments are Stripe (not Mollie); stripe-connect route/ service/file references corrected; CI section now reflects the inactive ci/ci.yml reality; storefront-first positioning. - README.md: frontend port is 4000 (was 5173); CI claim corrected; removed nonexistent /healthz endpoint claim. - env examples rebranded to Grainstash where safe (values provisioned by docker-compose left consistent with compose defaults). - 12 stale pre-Stripe/pre-rebrand review/spec docs moved to docs/archive/ with an explanatory README; CLAUDE.md and PRICING.md references updated.

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