fix(core): scope session lists to subpaths

[kitlangton]

Summary

Project-scoped session lists now honor the requested subpath, including sessions at that exact path and beneath it while excluding unrelated paths in the same project.

Test plan

• Added a regression covering an exact path, a nested path, and an unrelated sibling path
• Confirmed the regression failed before the query fix with 3 results instead of 2
• bun run test -- session-create.test.ts
• bun typecheck
• Repository pre-commit typecheck across packages