feat: add flexible region matching to servers API

- Add shared buildFlexibleRegionConditions() in utils.ts
- Add COUNTRY_NAME_TO_REGIONS mapping for country/city expansion
- Update servers.ts to use flexible region matching (korea, tokyo, japan, etc.)
- Update recommend.ts to use shared function (remove duplicate code)
- Fix servers GROUP BY to show all regions (it.id, r.id)
- Update CLAUDE.md with single-line curl examples

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

CLAUDE.md

@@ -90,9 +90,9 @@ Estimates monthly bandwidth based on use_case patterns:
 
 Heavy bandwidth (>1TB/month) prefers Linode for included bandwidth.
 
-### Flexible Region Matching (`candidates.ts`)
+### Flexible Region Matching (`utils.ts`)
 
-Region matching supports multiple input formats:
+Both `/api/recommend` and `/api/servers` use shared `buildFlexibleRegionConditions()`:
 ```sql
 LOWER(r.region_code) = ? OR
 LOWER(r.region_code) LIKE ? OR
@@ -100,7 +100,9 @@ LOWER(r.region_name) LIKE ? OR
 LOWER(r.country_code) = ?
 ```
 
-Valid inputs: `"korea"`, `"KR"`, `"seoul"`, `"ap-northeast-2"`, `"icn"`
+Valid inputs: `"korea"`, `"KR"`, `"seoul"`, `"tokyo"`, `"japan"`, `"ap-northeast-2"`, `"icn"`
+
+Country names are auto-expanded via `COUNTRY_NAME_TO_REGIONS` mapping.
 
 ### AI Prompt Strategy (`recommend.ts`)
 
@@ -151,29 +153,23 @@ OPENAI_API_KEY = "sk-..." # Set via wrangler secret
 
 ## Testing
 
+**Note**: Use single-line curl commands. Backslash line continuation (`\`) may not work in some environments.
+
 ```bash
 # Health check
-curl https://server-recommend.kappa-d8e.workers.dev/api/health
+curl -s https://server-recommend.kappa-d8e.workers.dev/api/health | jq .
 
-# Recommendation (e-commerce)
-curl -X POST https://server-recommend.kappa-d8e.workers.dev/api/recommend \
-  -H "Content-Type: application/json" \
-  -d '{
-    "tech_stack": ["php", "mysql"],
-    "expected_users": 1000,
-    "use_case": "e-commerce shopping mall",
-    "region_preference": ["korea"]
-  }'
+# Recommendation - nodejs/redis real-time chat (Japan)
+curl -s -X POST https://server-recommend.kappa-d8e.workers.dev/api/recommend -H "Content-Type: application/json" -d '{"tech_stack":["nodejs","redis"],"expected_users":1000,"use_case":"real-time chat","region_preference":["japan"]}' | jq .
 
-# Recommendation (analytics - heavier DB workload)
-curl -X POST https://server-recommend.kappa-d8e.workers.dev/api/recommend \
-  -H "Content-Type: application/json" \
-  -d '{
-    "tech_stack": ["postgresql"],
-    "expected_users": 500,
-    "use_case": "analytics dashboard",
-    "region_preference": ["japan"]
-  }'
+# Recommendation - php/mysql community forum (Korea)
+curl -s -X POST https://server-recommend.kappa-d8e.workers.dev/api/recommend -H "Content-Type: application/json" -d '{"tech_stack":["php","mysql"],"expected_users":800,"use_case":"community forum","region_preference":["korea"]}' | jq .
+
+# Recommendation - analytics dashboard (heavier DB workload)
+curl -s -X POST https://server-recommend.kappa-d8e.workers.dev/api/recommend -H "Content-Type: application/json" -d '{"tech_stack":["postgresql"],"expected_users":500,"use_case":"analytics dashboard","region_preference":["japan"]}' | jq .
+
+# Server list with filters (supports flexible region: korea, seoul, tokyo, etc.)
+curl -s "https://server-recommend.kappa-d8e.workers.dev/api/servers?region=korea&minCpu=4" | jq .
 ```
 
 ## Recent Changes
@@ -201,5 +197,6 @@ curl -X POST https://server-recommend.kappa-d8e.workers.dev/api/recommend \
 
 ### Code Quality
 - **Dead code removed**: Unused `queryVPSBenchmarks` function deleted
-- **DRY**: `DEFAULT_REGION_FILTER_SQL` shared between handlers
+- **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)