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/v0.2.106.ts

@@ -0,0 +1,13 @@
+import { VersionInfo } from '@start9labs/start-sdk'
+
+export const v_0_2_106 = VersionInfo.of({
+  version: '0.2.106:0',
+  releaseNotes: {
+    en_US:
+      "Tighten the mobile menu upgrade UX. v0.2.105 added two upgrade entries (Pro + Max) which forced free users to pick between tiers without seeing the comparison. Now Free signed-in users see a single 'Upgrade' entry that opens the buy modal at the tier picker so they can compare Pro vs Max side-by-side. Pro users see a single 'Upgrade to Max' entry that opens the modal pre-selected on Max. Max users see no upgrade entry. Anon/trial visitors continue through the existing Sign up → 3-tier modal flow.",
+  },
+  migrations: {
+    up: async ({ effects }) => {},
+    down: async ({ effects }) => {},
+  },
+})