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

server/test/subscription-reminders.test.js

@@ -0,0 +1,51 @@
+// Pure-logic tests for the expiry-reminder cadence: which reminder kind
+// (if any) applies to a relay subscription row right now. The send/dedup
+// path hits SQLite + SMTP and isn't unit-tested here; this nails the
+// decision that drives it.
+
+import { test, describe } from "node:test";
+import assert from "node:assert/strict";
+
+import { reminderKindFor } from "../subscription-reminders.js";
+
+const sub = (days_left, expired = false) => ({
+  tier: "pro",
+  expires_at: "2026-07-01T00:00:00.000Z",
+  expired,
+  days_left,
+});
+
+describe("reminderKindFor", () => {
+  test("upcoming: smallest crossed threshold wins", () => {
+    assert.equal(reminderKindFor(sub(8)), null); // beyond 7d
+    assert.equal(reminderKindFor(sub(7)), "upcoming_7d");
+    assert.equal(reminderKindFor(sub(5)), "upcoming_7d");
+    assert.equal(reminderKindFor(sub(2)), "upcoming_7d");
+    assert.equal(reminderKindFor(sub(1)), "upcoming_1d");
+    assert.equal(reminderKindFor(sub(0)), "upcoming_1d"); // expires today, not yet lapsed
+  });
+
+  test("lapsed: only within the lapsed window", () => {
+    assert.equal(reminderKindFor(sub(0, true)), "lapsed");
+    assert.equal(reminderKindFor(sub(-1, true)), "lapsed");
+    assert.equal(reminderKindFor(sub(-3, true)), "lapsed");
+    assert.equal(reminderKindFor(sub(-4, true)), null); // aged out (window=3)
+  });
+
+  test("null-safe / malformed input", () => {
+    assert.equal(reminderKindFor(null), null);
+    assert.equal(reminderKindFor({}), null);
+    assert.equal(reminderKindFor({ expired: false }), null); // no days_left
+    assert.equal(reminderKindFor({ days_left: "soon" }), null);
+  });
+
+  test("respects custom thresholds", () => {
+    const upcoming = [
+      { days: 14, kind: "upcoming_14d" },
+      { days: 3, kind: "upcoming_3d" },
+    ];
+    assert.equal(reminderKindFor(sub(14), { upcoming }), "upcoming_14d");
+    assert.equal(reminderKindFor(sub(3), { upcoming }), "upcoming_3d");
+    assert.equal(reminderKindFor(sub(15), { upcoming }), null);
+  });
+});