[protocols-core] Make strict ContractGraph mode mandatory for generated 1.0 app paths

[kang-heewon]

Problem

ContractGraph strict schema mode can detect missing response schemas, body schemas, and named parameter schemas before OpenAPI or RPC generation. Generated 1.0 app paths should not rely on compatibility-mode metadata for public contract artifacts.

Desired outcome

Generated 1.0 golden paths use strict ContractGraph validation before OpenAPI/RPC/client generation.

Acceptance criteria

• Enable strict ContractGraph schema/problem validation for generated 1.0 app paths.
• Ensure generated app smoke fails on strict ContractGraph diagnostics.
• Require OpenAPI and RPC codegen paths in generated apps to consume strict, error-free graphs.
• Keep compatibility mode available only through an explicit opt-out.
• Document strict mode versus compatibility mode for generated apps.