fix: harden token search with pagination, rate limiting and input validation

- Add configurable per-user token creation limit (max_user_tokens)
- Sanitize search input patterns to prevent expensive queries
- Add per-user search rate limiting (by user ID)
- Add pagination to search endpoint with strict page size cap
- Skip empty search fields instead of matching nothing
- Hide internal errors from API responses
- Fix Interface2String float64 formatting causing config parse failures
- Add float-string fallback in config system for int/uint fields

common/constants.go

@@ -175,6 +175,10 @@ var (
 
 	DownloadRateLimitNum            = 10
 	DownloadRateLimitDuration int64 = 60
+
+	// Per-user search rate limit (applies after authentication, keyed by user ID)
+	SearchRateLimitNum            = 10
+	SearchRateLimitDuration int64 = 60
 )
 
 var RateLimitKeyExpirationDuration = 20 * time.Minute