feat(orchestration-v2): subagent observability — data model and providers (1/4) - #4779

💭 Looking at the new files to verify import conventions — SubagentObservability.ts is a pure helper module that imports from "@t3tools/contracts" and uses namespace imports from effect libraries, which all follow the allowed patterns. The test file and migration file follow the same conventions. I'm checking whether any new code directly imports from "effect" or adds service creation patterns like Layer.succeed or ManagedRuntime, but this PR is mostly adapters and projections rather than new service definitions, so I don't expect to find those. Let me scan the touched files to confirm the import styles are consistent. I'm checking whether the contracts file imports the Effect namespace and uses Effect.succeed in the withDecodingDefault function, and I also noticed a test file naming mismatch where the describe label says "044" but the file is "045" — that's separate from the Effect conventions issue though. No violations found in the Effect service or import ordering. The TurnItemId import in ProviderAdapter.ts might be unused, but that's a lint concern rather than a convention issue. I need to format the response as JSON as required by the schema, though the instructions seem to be cut off mid-sentence.