ADC-754: expose typed rejection versus missing recovery policy

[wolf75222]

Scope

This source-only child of PR #627 makes the ADC-754 capability boundary programmatic and fail-closed.

• riemann:typed_failure_outcome reports the delivered common device-copyable FluxEvaluation path as partial: typed status, stability bound, reason code, reduction, and transactional rejection, with no solver substitution.
• riemann:prepared_recovery_policy reports ordered fallback policy, requested-versus-used solver metadata, counters, and restart provenance as unavailable, with the exact supported single-solver alternative and generated refusal message.
• focused tests lock both rows and documentation/changelog state the same non-claims.

Validation

• checkout-backed targeted Python batch: 14 passed
• Ruff: passed
• docs conformance: passed with one pre-existing stale-dependency warning
• git diff check: passed

Deliberate boundary

This PR does not implement a native Riemann recovery chain, fallback kernels, requested/used counters, restart metadata, GPU evidence, benchmarks, or the remaining degeneracy matrix. Those remain ADC-754 acceptance work and require native ABI/kernel changes.