Add proper locking/unlocking to WebDAV.

Tweak README, add one-click deploy for Digital Ocean and Render.

.do/deploy.template.yaml

@@ -0,0 +1,43 @@
+spec:
+  name: bewcloud
+  envs:
+    - key: BASE_URL
+      scope: RUN_AND_BUILD_TIME
+      value: ${app.PUBLIC_URL}
+  services:
+    - name: app
+      dockerfile_path: Dockerfile
+      git:
+        branch: main
+      http_port: 8000
+      instance_count: 1
+      instance_size_slug: basic-xs
+      routes:
+        - path: /
+      health_check:
+        http_path: /
+      source_dir: /
+      envs:
+        - key: POSTGRESQL_HOST
+          scope: RUN_AND_BUILD_TIME
+          value: ${db.HOSTNAME}
+        - key: POSTGRESQL_USER
+          scope: RUN_AND_BUILD_TIME
+          value: ${db.USERNAME}
+        - key: POSTGRESQL_PASSWORD
+          scope: RUN_AND_BUILD_TIME
+          value: ${db.PASSWORD}
+        - key: POSTGRESQL_DBNAME
+          scope: RUN_AND_BUILD_TIME
+          value: ${db.DATABASE}
+        - key: POSTGRESQL_PORT
+          scope: RUN_AND_BUILD_TIME
+          value: ${db.PORT}
+        - key: POSTGRESQL_CAFILE
+          scope: RUN_AND_BUILD_TIME
+          value: ""
+  databases:
+    - name: db
+      engine: PG
+      production: false
+      version: "15"