Add per-agent trace setup and isolated managed runs

[Stephen Belanger (Qard)]

Summary

• give Codex, Claude, OpenCode, and Pi independent persistent tracing settings files with one shared schema
• add invocation-only settings for concurrent bt trace run processes without mutating or falling back to global agent configuration
• add managed OpenCode and Pi launch support using their npm packages
• route both real-agent integration harnesses through managed run
• preserve structured destinations and profile/org selections in the JavaScript adapters

Validation

• make test
• cargo fmt --check --manifest-path bt-daemon/Cargo.toml
• cargo test --manifest-path bt-daemon/Cargo.toml --all-features --locked
• cargo clippy --manifest-path bt-daemon/Cargo.toml --all-features --all-targets --locked -- -D warnings
• OpenCode installed-package integration scenario with mock inference and ingest
• Pi managed-run integration scenario with mock inference and ingest

This PR is intentionally stacked on the Pi integration PR. The coordinated bt PR pins commit 952e2f26c8613d3fac82ca4999aae448a0b82139.