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/v0.2.87.ts

@@ -0,0 +1,12 @@
+import { VersionInfo } from '@start9labs/start-sdk'
+
+export const v_0_2_87 = VersionInfo.of({
+  version: '0.2.87:0',
+  releaseNotes: {
+    en_US: 'Clearer copy on the PodcastIndex credentials flow. Both the StartOS "Set PodcastIndex Credentials" action AND the in-app error when a Spotify URL fails now explicitly tell the operator that BOTH an API Key AND an API Secret are required (the most common reason Spotify resolution fails is leaving the Secret blank). Both credentials appear side-by-side on the api.podcastindex.org account page after free signup. The error message also reminds users that Apple Podcasts and Fountain links work without any PodcastIndex auth as a workaround.',
+  },
+  migrations: {
+    up: async ({ effects }) => {},
+    down: async ({ effects }) => {},
+  },
+})