fix(auth): make the Secure cookie flag fail-safe (default on)

secureCookies() keyed off NODE_ENV === "production", so an appliance deployed
without that var silently sent the auth + CSRF cookies WITHOUT the Secure flag —
the review's one Medium finding.

Now Secure is the DEFAULT and you only ever opt OUT: a misconfigured/forgotten env
can only make cookies more restrictive, never drop the flag. Dropped only on a
deliberate COOKIE_SECURE=0/false/no/off (or an explicit NODE_ENV=development as a
dev fallback). The LAN appliance that serves the SPA over plain http sets
COOKIE_SECURE=0 on purpose (a Secure cookie would never be sent over its http origin
and would lock operators out); a TLS deploy leaves it unset and gets Secure.

- auth.test.ts (5): pins the matrix — default Secure, production Secure, dev opt-out,
  COOKIE_SECURE falsey opts out, any other value opts in.
- .env.example documents COOKIE_SECURE (replaces the stale NODE_ENV cookie note).
- dev .env sets COOKIE_SECURE=0 (local http://localhost login keeps working).

server 80/80; build+lint green.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/server/src/auth.test.ts

@@ -0,0 +1,56 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { secureCookies } from "./auth.js";
+
+// The auth/CSRF cookies' Secure flag must be FAIL-SAFE: Secure by default, dropped only
+// on a deliberate opt-out. The old behaviour (Secure iff NODE_ENV==="production") leaked
+// cookies over plain HTTP on an appliance that forgot to set NODE_ENV — this pins the
+// corrected matrix.
+
+let savedCookieSecure: string | undefined;
+let savedNodeEnv: string | undefined;
+
+beforeEach(() => {
+  savedCookieSecure = process.env.COOKIE_SECURE;
+  savedNodeEnv = process.env.NODE_ENV;
+  delete process.env.COOKIE_SECURE;
+  delete process.env.NODE_ENV;
+});
+afterEach(() => {
+  restore("COOKIE_SECURE", savedCookieSecure);
+  restore("NODE_ENV", savedNodeEnv);
+});
+function restore(key: string, val: string | undefined) {
+  if (val === undefined) delete process.env[key];
+  else process.env[key] = val;
+}
+
+describe("secureCookies — fail-safe Secure flag", () => {
+  it("defaults to Secure when nothing is set (the appliance-forgot-NODE_ENV case)", () => {
+    expect(secureCookies()).toBe(true);
+  });
+
+  it("stays Secure in production", () => {
+    process.env.NODE_ENV = "production";
+    expect(secureCookies()).toBe(true);
+  });
+
+  it("drops Secure only for an explicit local-dev NODE_ENV", () => {
+    process.env.NODE_ENV = "development";
+    expect(secureCookies()).toBe(false);
+  });
+
+  it("COOKIE_SECURE override wins: falsey values opt OUT", () => {
+    for (const v of ["0", "false", "no", "off", "FALSE", " Off "]) {
+      process.env.COOKIE_SECURE = v;
+      expect(secureCookies(), `COOKIE_SECURE=${JSON.stringify(v)}`).toBe(false);
+    }
+  });
+
+  it("COOKIE_SECURE override wins: any other value opts IN (even in dev)", () => {
+    process.env.NODE_ENV = "development";
+    for (const v of ["1", "true", "yes", "on", ""]) {
+      process.env.COOKIE_SECURE = v;
+      expect(secureCookies(), `COOKIE_SECURE=${JSON.stringify(v)}`).toBe(true);
+    }
+  });
+});