Add Claude Code and Copilot plugin compatibility adapters

[Aaronontheweb]

Extend the managed plugin importer with Claude Code and GitHub Copilot compatibility formats.

This issue depends on #2134.
Issue #2134 owns the portable Agent Plugins 1.0.0 contract and the Codex compatibility adapter.

Scope

Add these explicit package formats:

Format	Input
Claude Code compatibility	.claude-plugin/plugin.json and supported declared skill paths
Copilot compatibility	Supported legacy root or .github/plugin/plugin.json fields

Reuse the Git acquisition, archive policy, source lifecycle, durable state, publication path, and content scanner boundary from #2134.
Add format adapters only.
Do not add another transport, scheduler, registry, or sync actor.

Selection rules

The default selector uses this order:

1. Agent Plugins 1.0.0
2. Codex compatibility
3. Claude Code compatibility
4. Copilot compatibility

An explicit format inspects only that format.
A selected invalid manifest fails without another format fallback.
The selector never merges declarations from separate manifests.

Compatibility adapters may support documented host differences.
They must not weaken the portable package contract.
Unknown execution fields cannot grant Netclaw authority.

Acceptance

• Each format has one valid fixture and one rejected fixture.
• Multi-manifest fixtures prove the selected precedence.
• Explicit format fixtures prove single-format inspection.
• Metadata aliases, defaults, and conflicts have explicit results.
• Unsupported components appear in diagnostics and remain inactive.
• Skills and bundled files use the existing logical skill tools.
• Actual public packages prove format compatibility.
• Documentation updates use docs(skills): document Agent Plugin formats and Git lifecycle netclaw-website#119.

This issue excludes marketplaces, private Git credentials, plugin subagents, MCP activation, hooks, LSP configuration, and host execution.
It does not claim full Claude Code or Copilot runtime compatibility.

References:

• https://agent-plugins.org/specification
• https://code.claude.com/docs/en/plugins-reference
• https://docs.github.com/en/copilot/reference/copilot-cli-reference/cli-plugin-reference