feat: containerize with Docker Compose + Ollama

Add full Docker setup so the app runs with a single 'docker compose up':

- Dockerfile: multi-stage build (node:22-alpine) for the SvelteKit app
- docker-compose.yml: three services:
  1. ollama: runs Ollama server with persistent volume for models
  2. model-init: one-shot container that pulls the configured model
     after Ollama is healthy, then exits
  3. app: the SvelteKit app, starts only after model-init succeeds
- .env.docker: set OLLAMA_MODEL to control which model is pulled
- .dockerignore: keeps image lean
- Switched adapter-auto to adapter-node (required for Docker/Node hosting)
- Updated README with Docker and local dev instructions

Usage:
  docker compose up              # default: llama3
  OLLAMA_MODEL=gemma2 docker compose up  # any Ollama model

Dockerfile

@@ -0,0 +1,27 @@
+# ---- Build stage ----
+FROM node:22-alpine AS build
+
+WORKDIR /app
+
+COPY package.json package-lock.json ./
+RUN npm ci
+
+COPY . .
+RUN npm run build
+
+# ---- Run stage ----
+FROM node:22-alpine AS run
+
+WORKDIR /app
+
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev
+
+COPY --from=build /app/build ./build
+COPY --from=build /app/package.json .
+
+ENV PORT=3000
+ENV HOST=0.0.0.0
+EXPOSE 3000
+
+CMD ["node", "build"]