feat: add web testing foundation with infra-backed suites (#349)

* feat: add web test framework with infra-backed suites

* fix: honor DATABASE_URL env in integration prepare script

* fix: apply web test review feedback

* fix: streamline web test infra lifecycle and workflow scope

docker/testing/compose.yml

@@ -0,0 +1,29 @@
+name: unsend-test
+
+services:
+  postgres:
+    image: postgres:16
+    restart: unless-stopped
+    environment:
+      POSTGRES_USER: usesend
+      POSTGRES_PASSWORD: password
+      POSTGRES_DB: usesend_test
+    ports:
+      - "54329:5432"
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U usesend -d usesend_test"]
+      interval: 5s
+      timeout: 5s
+      retries: 20
+
+  redis:
+    image: redis:7
+    restart: unless-stopped
+    command: ["redis-server", "--maxmemory-policy", "noeviction"]
+    ports:
+      - "6380:6379"
+    healthcheck:
+      test: ["CMD", "redis-cli", "ping"]
+      interval: 5s
+      timeout: 5s
+      retries: 20