Route remote project docs and repo skills through executor environment

[starr-openai]

Summary

• route project-doc discovery through the executor-backed environment
• route repo skill discovery and repo SKILL.md reads through the executor-backed environment
• add focused tests for remote project-doc, repo-skill discovery, and remote skill-body injection

Notes

• base: starr/pr-15034-app-server-command-exec
• this is the remaining core remote-context provenance slice on top of the existing workspace remap, app-server fs, and app-server command/exec PRs

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