fix(generator): preserve reviewed formal runtime contracts

[HaoyL666]

Summary

• restore raw provider Markdown fallback when Terraform Registry pages are unavailable
• preserve repo-authored formal scaffold contracts and refresh only generated placeholders
• align DistributedDatabase provider facts and safe GET/list request filters
• align AgentEndpoint mutation semantics and exclude the unused compartment-change operation
• add typed, validated repo-authored update-operation subsets while retaining the primary runtime update
• cover restricted manager security rendering for shared and dedicated service accounts

These are pre-upgrade correctness fixes discovered while exercising the SDK upgrade workflow. This PR does not change the pinned OCI Go SDK version.

Validation

• make formal-verify
• full go test -p 1 ./internal/formal/...
• full go test -p 1 ./internal/generator/...
• affected service-manager tests
• service-scoped generated-runtime reports for generativeaiagent and distributeddatabase
• make generated-mutability-gate
• go build -p 1 ./...
• go vet -p 1 ./...
• GOFLAGS=-p=1 make test including envtest; total coverage 39.6%