chore(trellis): update to 0.6.15

[leonfox28]

Summary

• Sync Trellis-managed skills, Codex agents/hooks, workflow, and runtime scripts to 0.6.15.
• Bring in task-path containment hardening and DeepSeek Harness workflow routing from the release.
• Preserve the project-specific monorepo packages and default package configuration.

Validation

• trellis update --dry-run (all managed files current; config.yaml intentionally customized)
• make doctor check-format lint
• umask 0077 && make test
• changed Python/TOML syntax validation
• git diff --check