fix: load reflection skill from system directory to avoid collision with user skills

[avoidwork]

Summary

The reflection skill must be loaded from a dedicated system directory (system-skills/) baked into the Docker image, separate from the user-mounted ./skills directory.

Motivation

The ./skills directory is user-mounted at runtime and may contain user-provided skills that could collide with or override system skills. The reflection skill is a built-in system skill that must always be available regardless of what the user mounts. Currently, skills/ is not copied into the Docker image (see Dockerfile line 39-43), meaning system skills are lost at build time and must be mounted — putting them in the same namespace as user skills.

Proposed Solution

1. Create system-skills/ directory at the project root (alongside skills/, src/, etc.)
2. Move system-critical skills (starting with reflection/) from skills/ to system-skills/
3. Update Dockerfile to copy system-skills/ into the image at build time:

   COPY system-skills/ ./system-skills/

4. Update skill discovery in src/skills/discoverer.js and src/skills/registry.js to scan both directories:
   • System scope: system-skills/ (baked into image, higher priority)
   • User scope: skills/ (mounted at runtime)
   • System skills shadow user skills with the same name (consistent with existing .agents/skills override logic)

Alternatives Considered

• Keeping system skills in skills/ with a naming convention (e.g., system-reflection) — rejected because user mounts could still override them
• Using environment variables to specify skill directories — adds configuration burden
• Bundling system skills into the package entry point — loses the progressive disclosure model

OpenSpec Note

This project uses OpenSpec for feature development. If this request is approved, I will:

1. Run /opsx:propose to generate a full proposal with specs and tasks
2. Iterate on the design before any code is written
3. Follow the task-driven implementation workflow

Additional Context

The reflection skill currently lives at skills/reflection/SKILL.md. The skill loading mechanism needs to be updated to resolve system skills from a separate, non-user-mounted path. This likely affects the skill discovery and loading pipeline wherever it resolves skill paths.

[avoidwork]

Fixed in #283.

[avoidwork]

Fixed in #416.