feat: add Special Situations SDK workflows

[daniel-scrivner]

Summary

• add grouped and flat Special Situations SDK helpers
• support raw Copy-for-LLM markdown exports
• cover routes, escaping, grouped delegation, and export behavior

Dependency

• archive issue helpers require datastream PR #1363 to be merged and deployed before production use

Validation

• gofmt -l client.go client_test.go
• go test -count=1 ./...
• adversarial GPT-5.5 High review: no material findings

Boundary

• public Special Situations only; no internal-only data capabilities are exposed

[daniel-scrivner]

Adversarial review record

• Pass 1 (GPT-5.5 High): no material findings.
• Accepted feedback: none.
• Rejected feedback: none.
• Residual dependency: archive helpers ship only after datastream PR #1363 is merged and deployed; this is documented in the SDK and PR.

[daniel-scrivner]

Underwriting-pack adversarial review record

• Pass 1 (GPT-5.5 High): accepted removal of unsupported query parameters and renamed the grouped helper from Underwrite to UnderwritingPack for API clarity.
• Pass 2 (GPT-5.5 High): no findings.
• Rejected feedback: none.
• Verification: gofmt, full Go tests, and diff hygiene passed.
• Dependency: this helper requires the API deployment containing datastream PR #1363.