security(cards): fail-secure dev-stub, headers, rate-limit, dsgvo audit

Behebt live verifiziertes Auth-Bypass auf cardecky-api.mana.how
(X-User-Id → founder-Tier) und zieht im selben Patch das fehlende
Operations-/Compliance-Fundament nach.

* Auth-Middleware fail-secure: opt-in via CARDS_AUTH_DEV_STUB="true"
  (war opt-out, Default true). Compose-Default flipped auf "false",
  NODE_ENV="production" für cards-api ergänzt, env-Template
  dokumentiert. vitest.config.ts + tests/setup.ts aktivieren den
  Stub gezielt für Test-Suiten.
* Security-Headers: Hono secureHeaders() in apps/api,
  SvelteKit hooks.server.ts mit X-Frame/X-Content-Type/Referrer/
  HSTS in apps/web. CSP bewusst ausgelassen — eigener Sprint.
* CORS-localhost-Whitelist nur außerhalb Prod.
* Rate-Limiting (in-memory sliding window, dependency-frei) auf
  share.receive 60/min/IP, media.upload 30/min/user,
  decks.generate + decks.from-image 10/min/user, dsgvo.* 10/min/IP.
* Health-Endpoint mit echter DB- und MinIO-Probe; /healthz bleibt
  Liveness, /healthz/details ist Readiness mit 503 bei Failure.
* DSGVO-Honesty: storage_ok + storage_error im Response (statt
  schluckend console.warn), Account-UI zeigt Fehler-Toast.
* Audit-Log: strukturierte JSON-Zeile (kind: "audit") auf stdout
  für /dsgvo/export, /dsgvo/delete, /me/export, /me/delete.
* Bug-Fix: duplizierte case "multiple-choice"-Clause in fsrs.ts.

Verifiziert: apps/api 17 Files / 104 Tests grün, apps/web check
0 errors. Deploy auf Mac Mini steht noch aus.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/api/tests/rate-limit.test.ts

@@ -0,0 +1,78 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { Hono } from 'hono';
+
+import {
+	rateLimit,
+	ipKey,
+	_resetRateLimitForTests,
+} from '../src/middleware/rate-limit.ts';
+
+describe('rateLimit middleware', () => {
+	beforeEach(() => {
+		_resetRateLimitForTests();
+	});
+
+	function buildApp(max: number) {
+		const app = new Hono();
+		app.use('/probe', rateLimit({ scope: 't', windowMs: 60_000, max, keyOf: ipKey }));
+		app.get('/probe', (c) => c.json({ ok: true }));
+		return app;
+	}
+
+	it('lässt Calls unter dem Limit durch und zählt Remaining runter', async () => {
+		const app = buildApp(3);
+		const ip = { 'X-Forwarded-For': '10.0.0.1' };
+
+		const r1 = await app.request('/probe', { headers: ip });
+		expect(r1.status).toBe(200);
+		expect(r1.headers.get('X-RateLimit-Remaining')).toBe('2');
+
+		const r2 = await app.request('/probe', { headers: ip });
+		expect(r2.status).toBe(200);
+		expect(r2.headers.get('X-RateLimit-Remaining')).toBe('1');
+
+		const r3 = await app.request('/probe', { headers: ip });
+		expect(r3.status).toBe(200);
+		expect(r3.headers.get('X-RateLimit-Remaining')).toBe('0');
+	});
+
+	it('antwortet 429 mit Retry-After wenn das Limit überschritten ist', async () => {
+		const app = buildApp(2);
+		const ip = { 'X-Forwarded-For': '10.0.0.2' };
+
+		await app.request('/probe', { headers: ip });
+		await app.request('/probe', { headers: ip });
+		const blocked = await app.request('/probe', { headers: ip });
+
+		expect(blocked.status).toBe(429);
+		expect(blocked.headers.get('Retry-After')).toBeTruthy();
+		const body = (await blocked.json()) as { error: string; retry_after_s: number };
+		expect(body.error).toBe('rate_limited');
+		expect(body.retry_after_s).toBeGreaterThan(0);
+	});
+
+	it('isoliert Buckets pro IP', async () => {
+		const app = buildApp(1);
+		const ipA = { 'X-Forwarded-For': '10.0.0.3' };
+		const ipB = { 'X-Forwarded-For': '10.0.0.4' };
+
+		await app.request('/probe', { headers: ipA });
+		const aBlocked = await app.request('/probe', { headers: ipA });
+		const bAllowed = await app.request('/probe', { headers: ipB });
+
+		expect(aBlocked.status).toBe(429);
+		expect(bAllowed.status).toBe(200);
+	});
+
+	it('benutzt nur den ersten X-Forwarded-For-Hop als Key', async () => {
+		const app = buildApp(1);
+		// Zwei Proxy-Hops im XFF — soll auf den Client-IP-Bucket fallen, nicht
+		// auf den Edge-IP-Bucket.
+		const headers1 = { 'X-Forwarded-For': '203.0.113.5, 10.0.0.9' };
+		const headers2 = { 'X-Forwarded-For': '203.0.113.5, 10.0.0.10' };
+
+		await app.request('/probe', { headers: headers1 });
+		const blocked = await app.request('/probe', { headers: headers2 });
+		expect(blocked.status).toBe(429);
+	});
+});