[the1mills]

Repairs the existing RS005 functional-programming conformance regression without raising the budget.

The current repository has 16 erased/untyped-error findings against a budget of 10. This PR removes exactly six:

• replaces the binary entrypoint's anyhow::Result/string-to-anyhow adapters with a typed MainError terminal boundary;
• replaces verify.rs's anyhow::Result alias with a typed TagVerifyError wrapping reqwest::Error;
• replaces the dormant four-transports Box setup signatures with a typed TransportRuntimeError.

No conformance budget is changed. The remaining 10 findings are the already-budgeted baseline. Runtime behavior is unchanged; the four-transports module remains unbuilt as documented.

[linear-code]

DEN-2859