refactor(api): tidy the api and shared packages (#2733)

fluxer_api/src/api/utils/IntegerOptions.ts

@@ -0,0 +1,16 @@
+export function readOptionalIntegerEnv(name: string): number | undefined {
+	const raw = process.env[name]?.trim();
+	if (raw === undefined || raw === '') return undefined;
+	const value = Number(raw);
+	if (!/^-?\d+$/.test(raw) || !Number.isSafeInteger(value)) {
+		throw new Error(`${name} must be a safe integer`);
+	}
+	return value;
+}
+
+export function requireIntegerInRange(name: string, value: number, min: number, max: number): number {
+	if (!Number.isSafeInteger(value) || value < min || value > max) {
+		throw new RangeError(`${name} must be an integer between ${min} and ${max}`);
+	}
+	return value;
+}