refactor: major architecture improvements and security hardening

## Security Fixes
- Fix XSS vulnerability in report.ts with escapeHtml()
- Add cache data integrity validation
- Add region_preference input validation (max 10 items, 50 chars each)
- Replace `any` types with `unknown` + type guards

## Architecture Refactoring
- Split utils.ts (801 lines) into 6 modules: http, validation, bandwidth, cache, ai, exchange-rate
- Extract AI logic to src/services/ai-service.ts (recommend.ts 49% reduction)
- Add Repository pattern: src/repositories/AnvilServerRepository.ts
- Reduce code duplication in DB queries

## New Features
- AI fallback: rule-based recommendations when OpenAI unavailable
- Vitest testing: 55 tests (utils.test.ts, bandwidth.test.ts)
- Duplicate server prevention in AI recommendations

## Files Added
- src/utils/{index,http,validation,bandwidth,cache,ai,exchange-rate}.ts
- src/services/ai-service.ts
- src/repositories/AnvilServerRepository.ts
- src/__tests__/{utils,bandwidth}.test.ts
- vitest.config.ts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/config.ts

@@ -78,7 +78,7 @@ export const i18n: Record<string, {
   invalidFields: string;
   techStackItemLength: string;
   schema: Record<string, string>;
-  example: Record<string, any>;
+  example: Record<string, unknown>;
   aiLanguageInstruction: string;
 }> = {
   en: {