feat: migrate pricing from legacy tables to anvil_pricing

- Replace pricing/instance_types/providers/regions with anvil_* tables
- Add real-time USD→KRW exchange rate conversion (open.er-api.com)
- Korean users (lang=ko) see KRW prices, others see USD
- Remove provider_filter parameter (now single provider: Anvil)
- Add ExchangeRateCache interface with 1-hour KV caching
- Update CLAUDE.md with new table structure and exchange rate docs

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

CLAUDE.md

@@ -51,14 +51,19 @@ src/
 
 ### D1 Database Tables (cloud-instances-db)
 
-- `providers` - Cloud providers (50+)
-- `instance_types` - Server specifications
-- `pricing` - Regional pricing
-- `regions` - Geographic regions
+**Primary tables (Anvil pricing)**:
+- `anvil_instances` - Anvil server specifications (vcpus, memory_gb, disk_gb, etc.)
+- `anvil_regions` - Anvil data center regions (name, display_name, country_code)
+- `anvil_pricing` - Anvil pricing data (monthly_price in USD)
+
+**Support tables**:
 - `tech_specs` - Resource requirements per technology (vcpu_per_users, min_memory_mb)
 - `vps_benchmarks` - Geekbench 6 benchmark data (269 records)
 - `benchmark_results` / `benchmark_types` / `processors` - Phoronix benchmark data
 
+**Legacy tables (no longer used)**:
+- `providers`, `instance_types`, `pricing`, `regions` - Old Linode/Vultr data
+
 ## Key Implementation Details
 
 ### DB Workload Multiplier (`recommend.ts`)
@@ -90,20 +95,26 @@ Estimates monthly bandwidth based on use_case patterns:
 
 Heavy bandwidth (>1TB/month) prefers Linode for included bandwidth.
 
-### Flexible Region Matching (`utils.ts`)
+### Flexible Region Matching
 
-Both `/api/recommend` and `/api/servers` use shared `buildFlexibleRegionConditions()`:
+Both `/api/recommend` and `/api/servers` use `buildFlexibleRegionConditionsAnvil()` for anvil_regions:
 ```sql
-LOWER(r.region_code) = ? OR
-LOWER(r.region_code) LIKE ? OR
-LOWER(r.region_name) LIKE ? OR
-LOWER(r.country_code) = ?
+LOWER(ar.name) = ? OR
+LOWER(ar.name) LIKE ? OR
+LOWER(ar.display_name) LIKE ? OR
+LOWER(ar.country_code) = ?
 ```
 
 Valid inputs: `"korea"`, `"KR"`, `"seoul"`, `"tokyo"`, `"japan"`, `"ap-northeast-2"`, `"icn"`
 
 Country names are auto-expanded via `COUNTRY_NAME_TO_REGIONS` mapping.
 
+### Exchange Rate Handling (`utils.ts`)
+
+- Korean users (lang=ko) see prices in KRW
+- Exchange rate fetched from open.er-api.com with 1-hour KV cache
+- Fallback rate: 1450 KRW/USD if API unavailable
+
 ### AI Prompt Strategy (`recommend.ts`)
 
 - Uses OpenAI GPT-4o-mini via Cloudflare AI Gateway (bypasses regional restrictions)
@@ -174,6 +185,13 @@ curl -s "https://server-recommend.kappa-d8e.workers.dev/api/servers?region=korea
 
 ## Recent Changes
 
+### Anvil Pricing Migration (Latest)
+- **New tables**: Migrated from `pricing` to `anvil_pricing` tables
+- **Provider**: Now uses "Anvil" as single provider (previously Linode/Vultr)
+- **Exchange rate**: Real-time USD→KRW conversion via open.er-api.com
+- **Removed**: `provider_filter` parameter no longer supported
+- **Currency handling**: Korean users see KRW, others see USD
+
 ### Architecture
 - **Modular architecture**: Split from single 2370-line file into organized modules
 - **Centralized config**: All magic numbers moved to `LIMITS` in config.ts
@@ -197,6 +215,4 @@ curl -s "https://server-recommend.kappa-d8e.workers.dev/api/servers?region=korea
 
 ### Code Quality
 - **Dead code removed**: Unused `queryVPSBenchmarks` function deleted
-- **DRY**: `DEFAULT_REGION_FILTER_SQL` and `buildFlexibleRegionConditions()` shared between handlers
-- **Name-based filtering**: Provider queries use names, not hardcoded IDs
 - **Flexible region matching**: Both endpoints support country/city/code inputs (korea, seoul, icn)