feat: add Dockerfile and GitLab CI/CD pipeline

Add Docker containerization with Deno and persistent SQLite volume.
Add GitLab CI pipeline with build and deploy stages.
Use SQLITE_PATH env var for configurable DB location.

Dockerfile

@@ -0,0 +1,15 @@
+FROM denoland/deno:2
+
+WORKDIR /app
+
+COPY deno.json deno.lock ./
+RUN deno install
+
+COPY . .
+RUN deno cache main.ts
+
+RUN mkdir -p /data
+VOLUME /data
+ENV SQLITE_PATH=/data/notes.db
+
+CMD ["deno", "run", "--allow-net", "--allow-read", "--allow-write", "--allow-env", "main.ts"]