Add explicit lifecycle commands for packaged agent skills

[tulayha]

Add opt-in commands for managing the agent skills shipped with VidXP. Start with one supported agent host.

Expected behavior:

• Provide install, update, status, and remove commands.
• Detect locally modified skill files and ask before replacing them.
• Keep host-specific folders and behavior behind a small adapter.
• Do not modify MCP or other agent configuration as a side effect.
• Use the skill files packaged by Package canonical agent workflow sources for host adapters #81 rather than requiring a repository checkout.

This issue depends on #81.

[tulayha]

Maintainer status update

The lifecycle outcome behind this issue remains part of the broader supported-host work, but the proposed universal VidXP command layer has been superseded by host-native plugin and skill lifecycle mechanisms.

For the first supported host, PR #111 publishes VidXP through the repository's Codex Git marketplace. Codex owns marketplace/plugin discovery, installation, refresh, inspection, and removal, while VidXP Desktop provides an explicit setup action for the selected local MCP runtime. Maintaining a parallel vidxp skills install/update/status/remove interface for the same lifecycle would duplicate the host's authority.

The same decision applies per host rather than assuming one universal filesystem installer. Claude Code has its own plugin marketplace lifecycle, hosted Claude skills use their platform lifecycle, and another host should receive a focused adapter only if its native mechanism cannot satisfy VidXP's opt-in, versioning, conflict-safety, and removal requirements.

Shared cross-host lifecycle guarantees remain tracked in #49. The canonical packaged workflow-source boundary remains tracked in #81.

Closing this issue as superseded by the host-native lifecycle architecture, not as an assertion that every supported-host adapter is already complete.