v0.13.0

portage check answers "can Portage buy from this store, and how?" from the CLI, with the same answer portage buy would act on.

• portage-cli 0.10.0 adds portage check URL [--json].
  • It reports a verdict (automated, webmcp, handoff or unsupported) and a plain-English next_step. Behind them it reports native UCP, the detected platform and recommended adapter gem, whether that gem is installed and which env vars are missing, hand-off-only status, and WebMCP status.
  • It wraps Portage::Ucp::Check and uses the same precedence as buy. The hand-off-only test moved into a shared HandoffHost, so the two commands can't disagree.
  • It only makes plain GETs, never builds a cart, and doesn't contact hand-off-only hosts at all. WebMCP is read only from a tab the Portage browser profile already has open on the store. It never launches a browser, so otherwise webmcp.status is skipped with a reason.
  • It exits 0 for automated and webmcp, 1 otherwise, and honours the --proxy* flags.
  • It now requires portage-ucp ~> 0.11.
• portage-ucp 0.11.0. Ucp::Check and portage-ucp-check now follow a homepage <link rel="ucp" href="..."> manifest pointer when /.well-known/ucp is missing, the same fallback buy uses. The report adds manifest_url when the manifest came from that link.
• buy plugin 0.8.0 adds a "Can Portage buy from this store?" step using portage check URL --json, used only when portage --help lists check.
• Docs. docs/checking-any-store.md now leads with portage check, and docs/api/cli-json.md, the CLI tutorial and both READMEs cover it.

The docs-only notes in portage-ucp-client and portage-ucp-webmcp stay unreleased.