Build the Cold Front staging commerce loop

[superposition]

What changed

• installs eight provider-neutral, copy-to-own commerce blocks from the pinned topcoat-blocks registry commit
• adds the fictional field-gear catalog, encrypted guest cart, US address checkout, deterministic staging quotes, and direct-USDC test routes
• adds Postgres migrations for inventory, reservations, orders, payment intents/events, fulfillment, and audit history
• adds Reown AppKit testnet connection for Solana Devnet, Ethereum Sepolia, and Optimism Sepolia when credentials exist
• adds replay-safe payment simulation and an explicit operator-approved USPS test-label handoff
• packages the Topcoat asset bundle for Railway and documents the production release gates

Shared block source is reviewed separately in superposition/topcoat-blocks#3. Cold Front keeps all styling, copy, data, provider policy, and mutations in this host.

Safety boundary

This is a staging workflow. It does not transfer real USDC, calculate provider-backed tax, buy real postage, or authorize operators for production. Production fails closed for checkout, catalog seeding, simulator routes, and missing persistent database/cookie configuration.

Validation

• ./scripts/check
• node --check crates/coldfront-ui/src/auth.js
• node --check crates/coldfront-ui/src/wallet.js
• Coatcheck: 49/49 cases passed, including serious/critical Axe gates
• live local HTTP workflow passed from catalog through cart, checkout, payment confirmation, receipt, and fixture-label approval
• forged CSRF mutation returned HTTP 400
• release binary served /health, /shop, and its generated stylesheet from the bundled assets

Review focus

• host-owned versus shared block boundary
• inventory reservation and payment replay behavior
• production fail-closed controls
• Railway/Postgres migration and asset-bundle packaging