fix: strip skills prefix from bare skill plugin export

[zeel2104]

Description

Fix duplicated skills/skills/ nesting in apm pack --format plugin for bare skill dependencies referenced through virtual paths like skills/<name>.

The exporter now normalizes bare-skill slugs before writing bundle paths, so dependencies such as github/awesome-copilot/skills/javascript-typescript-jest pack to skills/javascript-typescript-jest/ as expected. Added regression coverage for both the collector helper and the end-to-end plugin export path.

Fixes #719

Type of change

• Bug fix
• New feature
• Documentation
• Maintenance / refactor

Testing

• Tested locally
• All existing tests pass
• Added tests for new functionality (if applicable)

uv run python -m pytest tests/unit/test_plugin_exporter.py -q
uv run python -m pytest tests/unit/test_packer.py -q

[Copilot]

Pull request overview

Fixes incorrect skills/skills/ directory nesting when exporting plugin bundles for bare-skill dependencies referenced via virtual paths like skills/<name>, aligning packed output with plugin.json expectations and the plugin host directory convention.

Changes:

• Normalize bare-skill slugs derived from dependency virtual_path by stripping leading skills/ prefixes before emitting bundle paths.
• Add unit + end-to-end regression tests to ensure apm pack --format plugin places bare skills under skills/<skill-name>/ (no duplicated skills/).

Show a summary per file

File	Description
src/apm_cli/bundle/plugin_exporter.py	Adds _normalize_bare_skill_slug() and uses it in _collect_bare_skill() to prevent skills/skills/ nesting for virtual_path="skills/<name>".
tests/unit/test_plugin_exporter.py	Adds regression coverage for slug normalization and for the full plugin export path to ensure no duplicated skills/ directory is produced.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 0