feat(vscode): Markets button + full-screen marketplace view

[zo-sol]

Per the plan — VSCode first. Adds a Markets pill in the top bar (next to the wallet dropdown) that opens a full-screen skill marketplace.

What you get

• Markets button — a green pill beside the wallet dropdown (C3EP..krH ▾). Click → full-screen Markets view; the button shows an active state while open.
• Markets view — title, a search box, and a results grid. Opening it loads the popular list (empty query = supply-sorted); typing + Search filters.
• Skill cards — image slot (wand placeholder until NFT images land), name, description, supply (×count), and a Buy button that disables to Owned for skills you already hold.
• Back to chat returns to the conversation.

How it's wired (no new backend)

Reuses the shared market message contract (#26) end to end: searchSkills → searchResults, buySkill → buyResult, ownedSkills. The existing marketplaceEnv callbacks drive everything.

• searchResults now renders both the small skills-panel shop and the full Markets grid.
• ownedSkills re-renders the open view's Owned badges.
• buyResult refreshes whichever view is showing.

So a buy in the Markets view installs the skill (PR #20 path) and the card flips to Owned.

Scope / next

• VSCode-first intentionally. The mobile React surface gets its own design over the same contract next — that's the whole point of refactor(chat): single marketplace message contract shared by all surfaces #26 (shared wiring, per-surface look).
• Skill detail page (image + body + verify-before-buy) and categories are the next slices of On-chain marketplace layer: what's done + connect it to a shared human UI (CLI / VSCode / mobile) #16 (categories + NFT image need the small backend additions noted there). This PR is the browse → search → buy core.

Verify

• webview app script parses (it's an HTML string — no compile typecheck)
• test/test-skills.ts — 31/31 (incl. the contract↔webview agreement checks)
• tsc --noEmit clean (core + vscode)

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