feat: improve recommendation diversity and KRW rounding

- Add spec diversity: recommend Budget/Balanced/Premium tiers instead of same spec
- Add bandwidth-based filtering: prioritize servers with adequate transfer allowance
- Fix KRW rounding: server price 500원, TB cost 500원, GB cost 1원
- Add bandwidth warning to infrastructure_tips when traffic exceeds 2x included

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

CLAUDE.md

@@ -372,8 +372,13 @@ echo $REPORT_URL
 - `src/__tests__/{utils,bandwidth}.test.ts`
 - `vitest.config.ts`
 
+### Spec Diversity & Bandwidth-Based Filtering (Latest)
+- **Spec diversity**: No region specified → 3 different spec tiers (Budget/Balanced/Premium) from different regions
+- **Bandwidth-based filtering**: High bandwidth workloads (>2TB) automatically prioritize servers with adequate transfer allowance
+- **Bandwidth warning**: `infrastructure_tips` includes warning when estimated traffic exceeds included bandwidth by 2x+
+- **Previous issue fixed**: Was recommending same Basic 1GB spec × 3 (only region different), now recommends diverse specs
+
 ### Region Diversity & Bug Fixes
-- **Region diversity**: No region specified → same spec from 3 different regions for comparison
 - **Cache key fix**: `region_preference` now included in cache key
 - **Server ID fix**: Changed from `ai.id` (instance) to `ap.id` (pricing) for unique region+instance identification
 - **Prompt cleanup**: Removed obsolete Linode/Vultr/DigitalOcean references (Anvil only)