refactor: déplacer schema vers sql/schema.sql et sql.Schema()

sql/schema.sql

@@ -0,0 +1,7 @@
+-- Schema
+CREATE TABLE IF NOT EXISTS transactions (
+    id BIGINT PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
+    membre_id VARCHAR(7) NOT NULL,
+    given_at TIMESTAMP DEFAULT current_timestamp,
+    is_perpetual BOOLEAN NOT NULL
+);

sql/sql.go

@@ -0,0 +1,10 @@
+package sql
+
+import _ "embed"
+
+//go:embed schema.sql
+var schema string
+
+func Schema() string {
+	return schema
+}