fix subagent workspace navigation

[Victorzinn704]

Fixes #1130.

Summary

• Resolve subagent rows to the parent workspace when the child cwd is nested under that workspace.
• Keep the existing host-agent fallback when no workspace can be resolved.
• Add a regression test for nested subagent cwd navigation.

Test plan

• npm run build:workspace-deps --workspace=@getpaseo/app
• npm run test --workspace=@getpaseo/app -- src/utils/navigate-to-agent.test.ts
• npm run typecheck --workspace=@getpaseo/app
• npm run lint -- packages/app/src/utils/navigate-to-agent.ts packages/app/src/utils/navigate-to-agent.test.ts