feat: rate limiting + E2E crypto lifecycle test

Rate limiting (closes the last security gap #3):
- New RateLimiter: in-memory fixed-window IP-based limiter (std::sync::Mutex
  HashMap, no new deps). Configurable via RATE_LIMIT_MAX (default 100) +
  RATE_LIMIT_WINDOW_SECS (default 60) env vars.
- general_rate_limit_middleware now reads ClientIp from request extensions and
  rejects with 429 + Retry-After header when over the limit. Wired via
  from_fn_with_state in app.rs. Lived on AppState as Arc<RateLimiter>.
- Deleted the dead auth_rate_limit_middleware (never wired).
- 3 unit tests (allows up to N, independent IPs, window reset).

E2E crypto lifecycle test:
- Full zero-knowledge round-trip against jsdom's real Web Crypto: setup →
  encrypt → verify ciphertext → unlock with password → decrypt → recover via
  phrase → rewrap under new password → decrypt. Plus wrong-password/wrong-phrase
  failures and cross-user key isolation.
- Fixed wrapDek/unwrapDek: base64-encode raw DEK bytes (was using TextDecoder
  which produced non-base64), and make unwrapped DEK extractable (needed for
  rewrapDek to export).

Verified: backend 24 tests 0 warnings; frontend 24 tests, build clean.

web/normogen-web/src/crypto/crypto.e2e.test.ts

@@ -0,0 +1,101 @@
+import { describe, it, expect } from 'vitest';
+import {
+  setupEncryption,
+  unlockWithPassword,
+  unlockWithRecovery,
+  rewrapDek,
+  encryptJson,
+  decryptJson,
+  setEncKey,
+  clearEncKey,
+  hasEncKey,
+} from './index';
+
+describe('zero-knowledge crypto lifecycle', () => {
+  const password = 'my-secret-password';
+  const recoveryPhrase = 'my-recovery-phrase';
+  const sampleData = { name: 'Aspirin', dosage: '100mg', frequency: 'daily' };
+
+  it('full lifecycle: setup → encrypt → unlock → decrypt → recover → rewrap', async () => {
+    // 1. Setup (register): generate DEK, wrap under password + recovery.
+    const setup = await setupEncryption(password, recoveryPhrase);
+    expect(setup.dek).toBeDefined();
+    expect(setup.passwordWrappedDek.data).not.toBe('');
+    expect(setup.recoveryWrappedDek).toBeDefined();
+    expect(setup.recoveryKekHash).toBeDefined();
+
+    // 2. Encrypt data with the DEK.
+    const encrypted = await encryptJson(sampleData, setup.dek);
+    // Verify it's ciphertext, not plaintext.
+    expect(encrypted.data).not.toContain('Aspirin');
+    expect(encrypted.iv).not.toBe('');
+
+    // 3. Decrypt with the same DEK — round-trip.
+    const decrypted = await decryptJson<typeof sampleData>(encrypted, setup.dek);
+    expect(decrypted.name).toBe('Aspirin');
+    expect(decrypted.dosage).toBe('100mg');
+
+    // 4. Simulate page reload: DEK is lost.
+    clearEncKey();
+    expect(hasEncKey()).toBe(false);
+
+    // 5. Unlock with password (the unlock screen flow).
+    const unlockResult = await unlockWithPassword(password, setup.passwordWrappedDek);
+    setEncKey(unlockResult.dek);
+    expect(hasEncKey()).toBe(true);
+
+    // 6. The unlocked DEK can decrypt the same data.
+    const decryptedAfterUnlock = await decryptJson<typeof sampleData>(
+      encrypted,
+      unlockResult.dek,
+    );
+    expect(decryptedAfterUnlock.name).toBe('Aspirin');
+
+    // 7. Recover via recovery phrase (forgot password flow).
+    clearEncKey();
+    const recoveredDek = await unlockWithRecovery(
+      recoveryPhrase,
+      setup.recoveryWrappedDek!,
+    );
+    const decryptedAfterRecovery = await decryptJson<typeof sampleData>(
+      encrypted,
+      recoveredDek,
+    );
+    expect(decryptedAfterRecovery.name).toBe('Aspirin');
+
+    // 8. Rewrap under a new password (post-recovery).
+    const newPassword = 'my-new-password';
+    const rewrapped = await rewrapDek(recoveredDek, newPassword);
+    const unlockWithNew = await unlockWithPassword(newPassword, rewrapped);
+    const decryptedAfterRewrap = await decryptJson<typeof sampleData>(
+      encrypted,
+      unlockWithNew.dek,
+    );
+    expect(decryptedAfterRewrap.name).toBe('Aspirin');
+
+    clearEncKey();
+  });
+
+  it('wrong password fails to unlock', async () => {
+    const setup = await setupEncryption(password);
+    await expect(
+      unlockWithPassword('wrong-password', setup.passwordWrappedDek),
+    ).rejects.toThrow();
+  });
+
+  it('wrong recovery phrase fails to unlock', async () => {
+    const setup = await setupEncryption(password, recoveryPhrase);
+    await expect(
+      unlockWithRecovery('wrong-phrase', setup.recoveryWrappedDek!),
+    ).rejects.toThrow();
+  });
+
+  it('data encrypted under one key cannot be decrypted by another', async () => {
+    const setupA = await setupEncryption('user-a-password');
+    const setupB = await setupEncryption('user-b-password');
+    const encrypted = await encryptJson(sampleData, setupA.dek);
+
+    // User B's key cannot decrypt User A's data.
+    await expect(decryptJson(encrypted, setupB.dek)).rejects.toThrow();
+  });
+});