feat(docker): use pre-built GHCR image in docker-compose by default (#25)

docker-compose.yml now references ghcr.io/ulsklyc/oikos:latest so users
can start the app with a single 'docker compose up' without cloning or
building locally. The build: . entry is retained for contributors who
want to build from source with --build.

README Quick Start updated to document both the no-clone path (curl
docker-compose + .env.example) and the build-from-source path.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "oikos",
-  "version": "0.11.7",
+  "version": "0.11.8",
   "description": "Self-hosted family planner - calendar, tasks, shopping, meal planning, budget and more. Private, open-source, no subscription.",
   "main": "server/index.js",
   "type": "module",