fix: 优化 README 内容问题，优化绘图

services/plot.py

@@ -16,16 +16,70 @@ FONT = font_manager.FontProperties(fname=config.FONT_PATH)
 plt.rcParams["axes.unicode_minus"] = False
 
 
-def plot_line(times, values, title, ylabel, out_path):
-    plt.figure(figsize=(8, 4))
-    plt.plot(times, values, marker="o")
+def plot_line(
+    times,
+    normal_values,
+    title,
+    ylabel,
+    out_path,
+    free_values=None,  # ✅ 免费额度可选
+):
+    has_free = free_values is not None and len(free_values) > 0
 
-    plt.title(title, fontproperties=FONT)
-    plt.xlabel("时间", fontproperties=FONT)
-    plt.ylabel(ylabel, fontproperties=FONT)
+    if has_free:
+        fig, (ax1, ax2) = plt.subplots(2, 1, figsize=(8, 6), sharex=True)
+    else:
+        fig, ax1 = plt.subplots(1, 1, figsize=(8, 4))
+        ax2 = None
+
+    # ===== 普通额度 =====
+    ax1.plot(times, normal_values, marker="o")
+    ax1.set_title(
+        f"{title}（普通额度）" if has_free else title,
+        fontproperties=FONT,
+    )
+    ax1.set_ylabel(ylabel, fontproperties=FONT)
+    ax1.grid(True)
+
+    for i, (x, y) in enumerate(zip(times, normal_values)):
+        dy = 8 if i == 0 or y >= normal_values[i - 1] else -12
+
+        ax1.annotate(
+            f"{y}",
+            (x, y),
+            textcoords="offset points",
+            xytext=(0, dy),
+            ha="center",
+            fontsize=10,
+            fontproperties=FONT,
+        )
+
+    # ===== 免费额度（可选） =====
+    if has_free and ax2:
+        ax2.plot(times, free_values, marker="o", linestyle="--")
+        ax2.set_title(f"{title}（免费额度）", fontproperties=FONT)
+        ax2.set_xlabel("时间", fontproperties=FONT)
+        ax2.set_ylabel(ylabel, fontproperties=FONT)
+        ax2.grid(True)
+
+        for i, (x, y) in enumerate(zip(times, free_values)):
+            # 免费额度同样根据趋势决定标注方向
+            if i == 0:
+                dy = -8
+            else:
+                dy = -8 if y <= free_values[i - 1] else 8
+
+            ax2.annotate(
+                f"{y}",
+                (x, y),
+                textcoords="offset points",
+                xytext=(0, dy),
+                ha="center",
+                fontsize=8,
+                fontproperties=FONT,
+            )
 
     plt.xticks(rotation=45, fontproperties=FONT)
-    plt.grid(True)
     plt.tight_layout()
     plt.savefig(out_path, dpi=150)
     plt.close()