feat(risk): add generic observation v2 contract

[Pigbibi]

Summary

• add a parallel, hash-bound v2 risk observation and portable risk-profile selection contract
• bind candidate capability and benchmark policy separately; unsupported nonlinear, cash-flow, portfolio, and alternative-benchmark economics fail closed as PARKED
• add a v2 exact-object private ingress port with no SDK, listing, fallback, or write capability
• document the generic strategy/plugin migration boundary

Validation

• python -m unittest discover -s python/tests -v (245 tests passed)
• python python/scripts/build_config.py --check
• python python/scripts/runtime_settings.py validate
• python -m py_compile on new scripts and tests
• git diff --check

No platform target, strategy parameter, policy write, cloud adapter, or execution behavior changes.