Add multi-tenant cloud mode: self-serve purchase, credit metering, core-decoupling

Introduces RECAP_MODE=multi alongside single-mode self-host:
- Tenant auth + accounts (magic-link via System SMTP), per-tenant credit pool,
  anonymous trial minting with per-IP/-64 caps
- Self-serve Pro/Max purchase: inline Lightning (BTCPay) + card (Zaprite),
  prepaid 30-day periods, expiry-reminder emails
- Core-decoupling: relay owns cloud tier/expiry keyed by Recaps user-id
- SQLite (better-sqlite3) schema for multi-mode; filesystem unchanged for single
- StartOS actions/versions through 0.2.155

startos/versions/v0.2.81.ts

@@ -0,0 +1,12 @@
+import { VersionInfo } from '@start9labs/start-sdk'
+
+export const v_0_2_81 = VersionInfo.of({
+  version: '0.2.81:0',
+  releaseNotes: {
+    en_US: 'Pro buy flow polish for cloud tenants. The lite settings modal now has a Plan section showing tier (Pro/Max) + renewal date + days remaining, with the date highlighted yellow when expiry is within 14 days. Always-visible Renew button (purple/emphasized for unlicensed users or near-expiry users; muted otherwise). New "Take Recap Home" panel for licensed tenants — click "Get my license key" to reveal and copy your LIC1 string for use on a self-hosted Recap install. License key is fetched on demand via a new /api/account/license-key endpoint scoped to the calling user. Buy modal now auto-fills buyer_email from the signed-in user so the issued license carries it (helps Keysat admin lookups + support).',
+  },
+  migrations: {
+    up: async ({ effects }) => {},
+    down: async ({ effects }) => {},
+  },
+})