feat: hosted invoice page (real wallet) + merchant dashboard

pay-live is the hosted invoice page running the real WalletApiAdapter on
mainnet: no-param mode is a merchant tool that mints shareable invoice
links; with params it renders the checkout and confirms in-browser on the
invoice address's balance DELTA over public RPC (a pre-funded address can
never false-confirm). Bundled with pinned esbuild for GitHub Pages.

The dashboard drives the watcher's REST API (new GET /invoices + CORS):
create invoices, watch statuses flip, copy pay links. Verified live:
create → WATCHING → PAID against mainnet in one poll cycle.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>