fix(rate): type regional outcome validation failures (#4369)

[d-sorgcodexagent]

Outcome

Adds a narrow typed failure boundary for regional-ground trial validation. Validator exceptions now become GroundRegionalVariationFailed(stage=validation) with exception chaining and accepted-trial counts, while publishing no partial rows or dataset.

Verification

• 48 focused execution-job and regional-variation tests
• Ruff and format checks
• focused MyPy
• campaign manifest validation and 8 manifest tests
• documentation governance and structural gates
• successful-output SHA-256 remains 671e5fd6c59aa1c068f2a3bd608ff7ef58c585b7ee4897ca49ef4ae73743f6a0

Scope

This is stacked on PR #4370. It does not add a model authority, UI execution, or release claim. Issue #4369 remains open.

[dieterolson]

Consolidated into #4410. Closing to reduce CI/CD runner load.