feat: implement doctor schedule module, add detail fields to doctor profile, and integrate new appointment API client

appointment/CachedToken.java

@@ -0,0 +1,10 @@
+package vn.sis.appointment;
+
+import java.time.Instant;
+
+record CachedToken(String accessToken, String tokenType, Instant expiresAt) {
+    boolean isValid() {
+        return accessToken != null && !accessToken.isBlank()
+                && Instant.now().isBefore(expiresAt.minusSeconds(15));
+    }
+}