v1.15.0 — envelope unwrap on all mutations + schema relax

Invoices (and every resource) operable again through MCP mutations: {data,meta} envelope unwrapped on all mutations and single-object reads (#64, #65). Over-strict output schemas relaxed with anti-envelope tripwire test. verifactu_status honest 404 semantics. OAuth key provisioning fixed against CF origin (#56). Cursor marketplace manifest (#54) + ChatGPT submission kit refresh (#52). OpenAI-profile hardening (#57–#59), public surface scrub (#53, #60).

Full changelog: https://github.com/Frihet-io/frihet-mcp/blob/main/CHANGELOG.md