add db connection, refactor code, add db migration files

db/migrations/000003_create_systems.up.sql

@@ -0,0 +1,20 @@
+CREATE TABLE IF NOT EXISTS systems (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    text_id VARCHAR(256) NOT NULL,
+    title VARCHAR(256) NOT NULL,
+    description TEXT NOT NULL,
+    url VARCHAR(256) NOT NULL, 
+    download VARCHAR(256) NOT NULL,
+
+    created_at DATETIME NOT NULL DEFAULT current_timestamp
+);
+
+CREATE TABLE IF NOT EXISTS systems_compatibility (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    system_id INTEGER UNIQUE,
+    minimum VARCHAR(64) NOT NULL,
+    verified VARCHAR(64) NOT NULL,
+    maximum VARCHAR(64) NOT NULL,
+
+    FOREIGN KEY (system_id) REFERENCES systems(id) ON DELETE CASCADE
+);