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/app/api/v1/admin/settings/route.ts

@@ -0,0 +1,52 @@
+import { NextResponse } from 'next/server';
+
+import { withAuth, withPermission } from '@/lib/api/helpers';
+import { parseBody } from '@/lib/api/route-helpers';
+import { listSettings, upsertSetting, deleteSetting } from '@/lib/services/settings.service';
+import { upsertSettingSchema, deleteSettingSchema } from '@/lib/validators/settings';
+import { errorResponse } from '@/lib/errors';
+
+export const GET = withAuth(
+  withPermission('admin', 'manage_settings', async (_req, ctx) => {
+    try {
+      const data = await listSettings(ctx.portId);
+      return NextResponse.json({ data });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);
+
+export const PUT = withAuth(
+  withPermission('admin', 'manage_settings', async (req, ctx) => {
+    try {
+      const { key, value } = await parseBody(req, upsertSettingSchema);
+      const data = await upsertSetting(key, value, ctx.portId, {
+        userId: ctx.userId,
+        portId: ctx.portId,
+        ipAddress: ctx.ipAddress,
+        userAgent: ctx.userAgent,
+      });
+      return NextResponse.json({ data });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);
+
+export const DELETE = withAuth(
+  withPermission('admin', 'manage_settings', async (req, ctx) => {
+    try {
+      const { key } = await parseBody(req, deleteSettingSchema);
+      await deleteSetting(key, ctx.portId, {
+        userId: ctx.userId,
+        portId: ctx.portId,
+        ipAddress: ctx.ipAddress,
+        userAgent: ctx.userAgent,
+      });
+      return NextResponse.json({ success: true });
+    } catch (error) {
+      return errorResponse(error);
+    }
+  }),
+);