feat: scaffold Django multi-tenant project with 5 of 9 apps

Phase 1 scaffolding: config/, core/, base models, AES-256-GCM phone encryption, enums mirror

apps.tenant: Tenant + Domain (django-tenants)

apps.org: 11 models (OrgUnit hierarchy, Staff, audit logs)

apps.account: 4 models (UserAccount as AUTH_USER_MODEL, login/password tracking)

apps.permission: 7 models (RBAC + overrides + datascope + append-only changelog)

apps.region: 5 models (District, BusinessArea, MetroLine, MetroStation, School)

All migrations generated, manage.py check passes

core/encryption.py

@@ -0,0 +1,57 @@
+"""PII encryption per AGENTS.md §4.4: AES-256-GCM (NOT Fernet)."""
+import base64
+import hashlib
+import os
+
+from django.conf import settings
+from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+
+
+class PhoneEncryption:
+    """Encrypt phone numbers with AES-256-GCM, index via SHA-256 hash, display masked.
+
+    Storage: phone_encrypted = base64(nonce || ciphertext || tag)
+    Index:   phone_hash = sha256(plaintext) — used for equality lookups
+    Display: 138****1234
+    """
+
+    NONCE_LEN = 12
+
+    @staticmethod
+    def _key() -> bytes:
+        key_b64 = settings.PHONE_ENCRYPTION_KEY
+        if not key_b64:
+            raise RuntimeError(
+                "PHONE_ENCRYPTION_KEY is not configured. "
+                "Generate with: python -c 'import secrets,base64; print(base64.b64encode(secrets.token_bytes(32)).decode())'"
+            )
+        key = base64.b64decode(key_b64)
+        if len(key) != 32:
+            raise RuntimeError("PHONE_ENCRYPTION_KEY must decode to exactly 32 bytes (AES-256).")
+        return key
+
+    @classmethod
+    def encrypt(cls, phone: str) -> str:
+        if phone is None:
+            raise ValueError("phone cannot be None")
+        aesgcm = AESGCM(cls._key())
+        nonce = os.urandom(cls.NONCE_LEN)
+        ct = aesgcm.encrypt(nonce, phone.encode("utf-8"), None)
+        return base64.b64encode(nonce + ct).decode("ascii")
+
+    @classmethod
+    def decrypt(cls, ciphertext_b64: str) -> str:
+        raw = base64.b64decode(ciphertext_b64)
+        nonce, ct = raw[: cls.NONCE_LEN], raw[cls.NONCE_LEN :]
+        aesgcm = AESGCM(cls._key())
+        return aesgcm.decrypt(nonce, ct, None).decode("utf-8")
+
+    @staticmethod
+    def hash(phone: str) -> str:
+        return hashlib.sha256(phone.encode("utf-8")).hexdigest()
+
+    @staticmethod
+    def mask(phone: str) -> str:
+        if not phone or len(phone) < 7:
+            return "***"
+        return phone[:3] + "****" + phone[-4:]