fix(server): load Codex repo-local skills from the agent workspace

[lldxflwb]

Summary

Fix Codex skill discovery so repo-local .codex/skills are loaded from the agent workspace instead of the daemon process working directory.

Closes #401.

Root cause

Paseo launched codex app-server without setting its process cwd to the Codex session workspace. In practice, Codex app-server discovers repo-local skills from its own process cwd, so skills from the active repo were missing or replaced by skills from the daemon checkout.

The existing skills/list request also passed cwd as an array shape that did not affect Codex app-server discovery.

Changes

• launch codex app-server with the agent session cwd
• pass skills/list the session cwd as a string
• add a regression unit test for the skills/list request shape
• add a real e2e regression test proving repo-local .codex/skills/.../SKILL.md appears for the matching workspace

Validation

• npx vitest run src/server/agent/providers/codex-app-server-agent.test.ts src/server/agent/providers/codex-app-server-agent.features.test.ts
• npx vitest run src/server/agent/providers/codex-app-server-agent.e2e.test.ts -t "lists repo-local Codex skills from the session workspace"
• npm run typecheck
• npm run format

Scope

This change is Codex-only. It does not change Claude, OpenCode, or client schemas.

[lldxflwb]

Confirmed locally in a direct-connection Paseo setup.

I tested this against a patched daemon by creating two separate workspaces, each with a different repo-local Codex skill under .codex/skills/.../SKILL.md, then connecting directly to that daemon and creating one Codex agent per workspace.

Observed behavior after this fix:

• each Codex agent listed the repo-local skill from its own workspace
• skills from the daemon checkout were no longer leaking into other workspaces
• the targeted Codex regression tests added in this PR also pass locally

This was tested in direct mode against the local daemon, not only through the isolated e2e harness.