feat: add configurable watermark text in API settings

app/services/pdf_generator.py

@@ -192,7 +192,7 @@ class PianoPDF:
             self.elements.append(Spacer(1, 5*mm))
 
 
-def generate_pdf(plan_id, student_name, content, output_dir, rendered_report=None):
+def generate_pdf(plan_id, student_name, content, output_dir, rendered_report=None, watermark_text=None):
     """生成PDF文件"""
     os.makedirs(output_dir, exist_ok=True)
     output_path = os.path.join(output_dir, f"plan_{plan_id}.pdf")
@@ -272,7 +272,7 @@ def generate_pdf(plan_id, student_name, content, output_dir, rendered_report=Non
 
     # 水印函数（每页都绘制）
     def draw_watermark(c, doc):
-        if not CHINESE_FONT_OK:
+        if not watermark_text or not CHINESE_FONT_OK:
             return
         c.saveState()
         try:
@@ -283,7 +283,7 @@ def generate_pdf(plan_id, student_name, content, output_dir, rendered_report=Non
             c.translate(A4[0]/2, A4[1]/2)
             c.rotate(45)
             # 绘制水印文字（居中）
-            c.drawCentredString(0, 0, "仅供学习参考")
+            c.drawCentredString(0, 0, watermark_text)
         except Exception:
             pass  # 字体问题则跳过水印
         c.restoreState()