feat: zero-knowledge encryption Phase 1 — backend opaque + crypto module (WIP)

Backend: server can no longer read user data. All data blobs (medication,
appointment, profile name) are now opaque client-encrypted ciphertext — the
server stores and returns them verbatim, never deserializing the contents.

- Medication: removed MedicationData + flat MedicationResponse; new
  MedicationResponse echoes metadata + encrypted_data blob. Create/update
  accept opaque blobs (whole-blob replace). Update is no longer load-mutate-
  reserialize (server can't read the data).
- Appointment: same opaque treatment; status moved to a top-level document
  field so it remains filterable without decryption.
- Profile: name is now an opaque encrypted blob (name_data/name_iv). Auto-
  created profile on register starts with an empty name; client sets it.
- EncryptedFieldWire type shared across medication/appointment.

Frontend (partial): crypto module using Web Crypto API —
- crypto/keys.ts: double-PBKDF2 derivation (auth secret sent to server +
  encryption key kept in memory); in-memory key store (set/get/clear).
- crypto/cipher.ts: AES-GCM encrypt/decrypt + JSON convenience wrappers.
- crypto/index.ts: re-exports.

NOT YET DONE (frontend integration): auth store key derivation on login/register,
stores decrypt-on-load/encrypt-on-write, types update, UI components wired,
crypto round-trip tests, ADR. This commit is a verified checkpoint — backend
builds clean (21 tests, 0 warnings); frontend crypto module exists but is not
yet wired into the data flow.

web/normogen-web/src/crypto/index.ts

@@ -0,0 +1,16 @@
+export {
+  deriveAuthAndEncKeys,
+  setEncKey,
+  getEncKey,
+  clearEncKey,
+  hasEncKey,
+  AUTH_SALT,
+  ENC_SALT,
+} from './keys';
+export {
+  encrypt,
+  decrypt,
+  encryptJson,
+  decryptJson,
+  type CipherPayload,
+} from './cipher';