Move fleet retention and concurrency controls into Settings

Persist settings in SQLite, import legacy environment values once, and apply changes to cleanup and deployment queues without restarting.

Closes #51

src/lib/fleet-settings.ts

@@ -0,0 +1,34 @@
+export interface FleetSettings {
+    deployKeepDays: number;
+    restartConcurrency: number;
+    createConcurrency: number;
+}
+
+export const defaultFleetSettings: FleetSettings = {
+    deployKeepDays: 7,
+    restartConcurrency: 1,
+    createConcurrency: 1
+};
+
+export const fleetSettingLabels: Record<keyof FleetSettings, string> = {
+    deployKeepDays: 'Campaign history retention',
+    restartConcurrency: 'Concurrent restarts',
+    createConcurrency: 'Concurrent server startups'
+};
+
+export function validateFleetSettings(input: unknown): FleetSettings {
+    if (!input || typeof input !== 'object' || Array.isArray(input)) throw new Error('Provide fleet settings.');
+    const values = input as Record<string, unknown>;
+    for (const key of Object.keys(values)) {
+        if (!Object.hasOwn(defaultFleetSettings, key)) throw new Error(`Unknown setting: ${key}`);
+    }
+    for (const key of Object.keys(defaultFleetSettings) as (keyof FleetSettings)[]) {
+        const value = values[key];
+        if (typeof value !== 'number' || !Number.isSafeInteger(value) || value < 1) {
+            throw new Error(`${fleetSettingLabels[key]} must be a positive whole number.`);
+        }
+        if (key === 'deployKeepDays' && value > 36500) throw new Error('Campaign history retention must be at most 36500 days.');
+    }
+    return { deployKeepDays: values.deployKeepDays as number, restartConcurrency: values.restartConcurrency as number,
+        createConcurrency: values.createConcurrency as number };
+}