Skill discovery reports missing per-agent repo/skills path

## Description

Skill discovery reports the expected `bailian-cli` collision, but then also tries to load a per-agent memory skill directory that does not exist.

## Output

```text
[Skill conflicts]
"bailian-cli" collision:
✓ auto (project) ~\.omo\skills\bailian-cli\SKILL.md
✗ ~\.agents\skills\bailian-cli\SKILL.md (skipped)
~\.omo\memory\agents\yejun-d09b8d51\repo\skills
skill path does not exist
```

## Expected behavior

A missing optional per-agent skill directory should be ignored (or created before skill discovery) instead of being reported as an error after the valid skill collision.

## Environment

- Windows_NT 10.0.26200
- `bailian-cli` is present in both `~\.omo\skills` and `~\.agents\skills`

Reproduce the reported Windows skill-discovery output using the paths and collision shown in the issue, then trace the skill discovery entry point that handles the per-agent memory repository. Done means the missing optional directory is ignored or created before discovery, while the valid bailian-cli collision is still reported.

Written by the indexing model from the issue text.