fix(database): correct metrics and improve error handling

- Fix metrics double-counting: track deltas for WaitCount/WaitDuration
  instead of adding cumulative values each tick
- Replace fmt.Printf with structured logging in pool monitor
- Add PoolOptions validation (MaxConns > 0, MinConns >= 0)
- Warn when DATABASE_URI overrides non-default PoolOptions
- Improve findAndParseConfig to report all tried files and errors
- Remove dead code in pgdb/config.go (unreachable host default)
- Fix errcheck lint issues for file.Close() calls
- Add context parameter to OpenDBMonitor() (breaking change)

database/pgdb/config.go

@@ -27,15 +27,10 @@ func CreatePoolConfig(cfg *database.PostgresConfig) (*pgxpool.Config, error) {
 		"require": true, "verify-ca": true, "verify-full": true,
 	}
 	if cfg.SSLMode != "" && !validSSLModes[cfg.SSLMode] {
-		return nil, fmt.Errorf("postgres: invalid sslmode: %s", cfg.SSLMode)
-	}
-
-	// Set defaults
-	host := cfg.Host
-	if host == "" {
-		host = "localhost"
+		return nil, fmt.Errorf("postgres: invalid sslmode: %s (valid: disable, allow, prefer, require, verify-ca, verify-full)", cfg.SSLMode)
 	}
 
+	// Apply defaults for optional fields (host is validated as required above)
 	port := cfg.Port
 	if port == 0 {
 		port = 5432
@@ -49,7 +44,7 @@ func CreatePoolConfig(cfg *database.PostgresConfig) (*pgxpool.Config, error) {
 	// Build connection string WITHOUT password
 	// We'll set the password separately in the config
 	connString := fmt.Sprintf("host=%s port=%d user=%s dbname=%s sslmode=%s",
-		host, port, cfg.User, cfg.Name, sslmode)
+		cfg.Host, port, cfg.User, cfg.Name, sslmode)
 
 	// Parse the connection string
 	poolConfig, err := pgxpool.ParseConfig(connString)