Implement KCA: web reimplementation of XCA PKI workflows

- kaya backend with OIDC sessions, API tokens, Postgres/Tortoise models
- AES-256-GCM private key storage and full certificate/CSR/CRL domain logic
- Sycamore/WASM SPA for vaults, keys, requests, certificates, CRLs and templates
- imports/exports, XCA .xdb migration, Docker Compose stack and tests

server/tests/helpers/api.py

@@ -0,0 +1,17 @@
+"""In-process HTTP client for the app."""
+from __future__ import annotations
+
+import contextlib
+from typing import AsyncIterator
+
+from httpx import ASGITransport, AsyncClient
+
+from kca.app import app, tortoise_mixin
+
+
+@contextlib.asynccontextmanager
+async def api_client() -> AsyncIterator[AsyncClient]:
+    await tortoise_mixin.ensure_context()
+    transport = ASGITransport(app=app)
+    async with AsyncClient(transport=transport, base_url="http://127.0.0.1") as client:
+        yield client