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/v0.2.123.ts

@@ -0,0 +1,13 @@
+import { VersionInfo } from '@start9labs/start-sdk'
+
+export const v_0_2_123 = VersionInfo.of({
+  version: '0.2.123:0',
+  releaseNotes: {
+    en_US:
+      "Drop the per-speaker turn count from the Speakers legend. A 90-min interview with 1000+ turns per speaker was emitting numbers too big to mean anything to viewers; speaking time (24:42, 65:37, 3s) is the actually-useful per-speaker fact and lets a glance distinguish 'main host' from 'brief interlude'. Same legend layout, just the noisy field removed.",
+  },
+  migrations: {
+    up: async ({ effects }) => {},
+    down: async ({ effects }) => {},
+  },
+})