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/v0.2.107.ts

@@ -0,0 +1,13 @@
+import { VersionInfo } from '@start9labs/start-sdk'
+
+export const v_0_2_107 = VersionInfo.of({
+  version: '0.2.107:0',
+  releaseNotes: {
+    en_US:
+      "Cleaner sign-in form. Removed the 'you@example.com' placeholder from the email field on both /auth.html and the in-app tier signup modal (it was clutter that some users read as a real suggested value). Removed the 'Leave blank to receive a sign-in link' placeholder from the password field on /auth.html — the same guidance already appears in the helper paragraph below the submit button, so the placeholder was duplicative.",
+  },
+  migrations: {
+    up: async ({ effects }) => {},
+    down: async ({ effects }) => {},
+  },
+})