feat(agent): ship the versioned session contract

[e54-bot]

Summary

• Define and version wright-agent/v1, with schemas and capability negotiation for every ToolService operation.
• Add wright serve over stdio and JSON-RPC, routing workflow operations through the shared service while retaining the standalone alias.
• Document the contract and extend packaged-binary smoke coverage to negotiate capabilities and run a structured check.

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace --all-targets --all-features
• cargo test -p wright-cli --test agent_contract --test serve
• cargo build --locked --release -p wright-cli -p wright-lsp
• python3 scripts/smoke-native.py --wright target/release/wright --wright-lsp target/release/wright-lsp --version 0.2.40
• python3 scripts/test-distribution-install-sh.py

Fixes #407

[Teakowa]

Two contract-correctness issues block wright-agent/v1 from satisfying #407. CI is green, and the transport/distribution work otherwise stays within scope.