feat: add virtuals-protocol-acp skill (cherry-pick of #43)

[kevarifin14]

Cherry-pick of #43 (by @tonyagents) onto current main, with marketplace.json conflict resolved.

Closes #43

Why this PR

#43 was A+ but had merge conflicts with #11, #31, and earlier merges to .claude-plugin/marketplace.json. This PR carries the same content with the conflict resolved, so it can merge cleanly.

Review reference

My A+ review of the original is at #43. Verification summary:

• Virtual-Protocol/openclaw-acp v0.4.0 verified — all ~40 acp CLI commands real (setup, browse, job create/status/pay, wallet address/balance, agent list/create/switch, token launch/info, sell init/create/delete, serve start/stop/deploy railway, social twitter, bounty create/list/poll, profile show/update, resource query)
• Own virtuals-protocol-skills plugin block in marketplace.json
• Frontmatter complete (name, description, tags)
• No code; pure instructional

Test plan

• CI checks pass
• Marketplace entry resolves correctly

Credit: @tonyagents (original author of #43)