Add batch and child run_agents metadata fields

[warp-agent-staging]

Description

Add sensitive string metadata maps to RunAgents (batch defaults) and AgentRunConfig (child overrides). Regenerate the checked-in Go bindings; Rust and TypeScript remain build-generated.

Justification

Part of REMOTE-3439. Orchestrators need to label children without changing parent inheritance.

Requester context: “Yep, I think the idea is roughly to add metadata as an option that you can set in the run_agents tool. That would then populate the metadata field on the ai_task for the child run. Then in the subagents execution, we'd resolve the metadata associated with that run and flatten it to injected vars.”

Companions: server #19546, client #16396, and worker #167.

Optional/additive fields preserve old-client compatibility. Merge and environment validation live in the client/server consumers, not the protocol. Consumers pin commit 6b33333f17ae74f1d18769672d6594d095b3f3da; merge this dependency first.

Validation passed: ./script/generate -a multi_agent -v v1, Go binding tests, npm ci, npm run generate:ts, and cargo build (writable temporary Cargo caches). Go generation used protoc 36.1 and protoc-gen-go 1.36.6.

Sensitive Fields

• I have ensured that all string fields that contain sensitive information are marked as sensitive.

Plans:

• Child-run metadata propagation and hosted setup environment

[warp-agent-staging]

This PR was generated with Warp.

Comment @warp-staging-factory on this PR to send it follow-up work.