Implement admin ports and system settings management

- Port CRUD: list, create, update with branding, currency, timezone
- System settings: upsert key-value pairs per port with known settings UI
  (AI feature flags, invoice discount, pipeline weights, berth rules)
- Settings manager with toggle switches, number inputs, and JSON editors
- Replace both stub pages with real implementations

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/validators/settings.ts

@@ -0,0 +1,14 @@
+import { z } from 'zod';
+
+export const upsertSettingSchema = z.object({
+  key: z.string().min(1).max(100),
+  value: z.unknown(),
+});
+
+export type UpsertSettingInput = z.infer<typeof upsertSettingSchema>;
+
+export const deleteSettingSchema = z.object({
+  key: z.string().min(1).max(100),
+});
+
+export type DeleteSettingInput = z.infer<typeof deleteSettingSchema>;