Flatten to three packages + extract mizan-runtime

packages/
  mizan-runtime/   Framework-agnostic state engine (~150 lines)
                   Context registry, batched invalidation, fetch primitives
  mizan-django/    Django server adapter (was packages/mizan-rpc/adapters/django/)
                   Codegen moved to mizan-django/generate/
  mizan-react/     React adapter (was packages/mizan-csr/adapters/react/)

Removed premature abstractions: mizan-ast, mizan-schema, mizan-rpc,
mizan-csr, mizan-ssr stub packages. The actual architecture is three
concrete packages, not five abstract layers.

mizan-runtime implements the v1 spec: registerContext with params,
scoped invalidation via microtask batching, server-driven invalidation
from mutation responses, mizanFetch for context bundles, mizanCall for
mutations.

264 Django + 33 React tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/mizan-django/tests/settings.py

@@ -0,0 +1,46 @@
+"""
+Django settings for running mizan's test suite standalone.
+
+Usage:
+    cd django/
+    pip install -e ".[dev]"
+    pytest
+"""
+
+SECRET_KEY = "test-secret-key-for-standalone-tests-only"
+
+DEBUG = True
+
+DATABASES = {
+    "default": {
+        "ENGINE": "django.db.backends.sqlite3",
+        "NAME": ":memory:",
+    }
+}
+
+INSTALLED_APPS = [
+    "django.contrib.auth",
+    "django.contrib.contenttypes",
+    "django.contrib.sessions",
+    "mizan",
+    "tests",
+]
+
+AUTH_USER_MODEL = "tests.EmailUser"
+
+ROOT_URLCONF = "tests.urls"
+
+DEFAULT_AUTO_FIELD = "django.db.models.BigAutoField"
+
+# JWT settings for test_auth.py (can be overridden per-class with @override_settings)
+JWT_PRIVATE_KEY = "test-secret-key-for-testing-only"
+JWT_ALGORITHM = "HS256"
+
+# Session engine (for test_auth.py SessionStore usage)
+SESSION_ENGINE = "django.contrib.sessions.backends.db"
+
+MIDDLEWARE = [
+    "django.contrib.sessions.middleware.SessionMiddleware",
+    "django.middleware.csrf.CsrfViewMiddleware",
+    "django.contrib.auth.middleware.AuthenticationMiddleware",
+]