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.

src/data/db.ts

@@ -1,7 +1,7 @@
 import { DB } from "https://deno.land/x/sqlite/mod.ts";
 import type { Note } from "./note"
 
-export const db = new DB("notes.db");
+export const db = new DB(Deno.env.get("SQLITE_PATH") ?? "notes.db");
 
 export const upsertNote = async (note: Note) => {
   db.query(