fix: address all final review findings for Phase 3

- CRITICAL: Fix command injection in discoveryService (execFile instead
  of exec, path validation regex)
- CRITICAL: Add Zod validation on discover API endpoint
- HIGH: Add Zod validation on discover/approve endpoint
- HIGH: Add array length limits to import schema (1000/100/100)
- HIGH: Fix theme broadcast echo loop (setTimeout vs queueMicrotask)
- MEDIUM: Singleton BroadcastChannel instead of create-per-send
- MEDIUM: Exclude sensitive APIs from service worker cache
- MEDIUM: Fix TypeScript cast errors in exportService tests

src/routes/api/admin/discover/approve/+server.ts

@@ -1,20 +1,19 @@
 import { json } from '@sveltejs/kit';
+import { z } from 'zod';
 import type { RequestHandler } from './$types';
 import { requireAdmin } from '$lib/server/middleware/authorize.js';
 import { create } from '$lib/server/services/appService.js';
 import { success, error } from '$lib/server/utils/response.js';
 
-interface ApproveServiceInput {
-	readonly name: string;
-	readonly url: string;
-	readonly source: 'docker' | 'traefik';
-	readonly icon?: string;
-	readonly description?: string;
-}
-
-interface ApproveBody {
-	readonly services: readonly ApproveServiceInput[];
-}
+const approveSchema = z.object({
+	services: z.array(z.object({
+		name: z.string().min(1),
+		url: z.string().url(),
+		source: z.enum(['docker', 'traefik']),
+		icon: z.string().optional(),
+		description: z.string().optional()
+	})).min(1).max(100)
+});
 
 /**
  * POST /api/admin/discover/approve — Approve discovered services and create app entries. Admin only.
@@ -24,26 +23,24 @@ interface ApproveBody {
 export const POST: RequestHandler = async (event) => {
 	const user = requireAdmin(event);
 
-	let body: ApproveBody;
+	let rawBody: unknown;
 	try {
-		body = await event.request.json();
+		rawBody = await event.request.json();
 	} catch {
 		return json(error('Invalid JSON body'), { status: 400 });
 	}
 
-	if (!body.services || !Array.isArray(body.services) || body.services.length === 0) {
-		return json(error('At least one service must be provided for approval'), { status: 400 });
+	const parsed = approveSchema.safeParse(rawBody);
+	if (!parsed.success) {
+		return json(error(`Validation failed: ${parsed.error.issues.map((i) => i.message).join(', ')}`), { status: 400 });
 	}
 
+	const body = parsed.data;
+
 	const created: string[] = [];
 	const errors: string[] = [];
 
 	for (const service of body.services) {
-		if (!service.name || !service.url) {
-			errors.push(`Skipped invalid service entry (missing name or url)`);
-			continue;
-		}
-
 		try {
 			const app = await create({
 				name: service.name,