Improve request logging and make health check lightweight

- Log slow requests (>1s) at WARNING level with slow=true flag
- Log request timeouts at WARNING level in TimeoutMiddleware
- Replace heavy GetStatsContext with lightweight Ping in health check
- Add Ping method to database interface (SELECT 1)

internal/server/middleware.go

@@ -168,7 +168,7 @@ func (tw *timeoutWriter) markWritten() {
 // The timeout parameter specifies the maximum duration allowed for request processing.
 // The returned middleware handles panics from the wrapped handler by re-panicking
 // after cleanup, and prevents concurrent writes to the response after timeout occurs.
-func TimeoutMiddleware(timeout time.Duration) func(http.Handler) http.Handler {
+func TimeoutMiddleware(timeout time.Duration, logger *slog.Logger) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			startTime := time.Now()
@@ -204,6 +204,14 @@ func TimeoutMiddleware(timeout time.Duration) func(http.Handler) http.Handler {
 				tw.markWritten() // Prevent the handler from writing after timeout
 				execTime := time.Since(startTime)
 
+				// Log the timeout as a warning
+				logger.Warn("Request timeout",
+					"method", r.Method,
+					"path", r.URL.Path,
+					"duration_ms", execTime.Milliseconds(),
+					"remote_addr", r.RemoteAddr,
+				)
+
 				// Write directly to the underlying writer since we've marked tw as written
 				// This is safe because markWritten() prevents the handler from writing
 				tw.mu.Lock()
@@ -350,10 +358,16 @@ func RequestLoggerMiddleware(logger *slog.Logger) func(http.Handler) http.Handle
 			// Log request completion
 			duration := time.Since(start)
 			logLevel := slog.LevelInfo
+
+			// Slow query threshold (1 second)
+			const slowQueryThreshold = 1 * time.Second
+
 			if sw.statusCode >= http.StatusInternalServerError {
 				logLevel = slog.LevelError
 			} else if sw.statusCode >= http.StatusBadRequest {
 				logLevel = slog.LevelWarn
+			} else if duration >= slowQueryThreshold {
+				logLevel = slog.LevelWarn
 			}
 
 			logger.Log(r.Context(), logLevel, "HTTP request completed",
@@ -362,6 +376,7 @@ func RequestLoggerMiddleware(logger *slog.Logger) func(http.Handler) http.Handle
 				"status", sw.statusCode,
 				"duration_ms", duration.Milliseconds(),
 				"remote_addr", r.RemoteAddr,
+				"slow", duration >= slowQueryThreshold,
 			)
 		})
 	}