feat: application icon for Windows taskbar + exe

- scripts/gen_icon.py: generates 256x256 SSH client icon (dark terminal
  window with >_ prompt and SSH connection nodes), outputs multi-size
  ICO (16-256px) + PNG
- resources/icon.ico + icon.png: generated icon files
- main.py: _get_icon_path() searches _MEIPASS (onefile), exe dir, source
  dir; sets app + window icon
- build.spec: bundles icon files via datas=, sets exe icon=icon.ico
- Windows taskbar will now show the custom icon instead of default PyInstaller icon

scripts/gen_icon.py

@@ -0,0 +1,130 @@
+"""
+生成 SSHClient 应用图标
+- 深色圆角方块背景
+- 终端窗口 + >_ 提示符 + SSH 连接线
+输出: resources/icon.ico (多尺寸) + resources/icon.png (256x256)
+"""
+import os
+from PIL import Image, ImageDraw, ImageFont
+
+OUT_DIR = os.path.join(os.path.dirname(__file__), "resources")
+os.makedirs(OUT_DIR, exist_ok=True)
+
+SIZE = 256
+
+def draw_icon(size: int) -> Image.Image:
+    """绘制指定尺寸的图标"""
+    img = Image.new("RGBA", (size, size), (0, 0, 0, 0))
+    d = ImageDraw.Draw(img)
+
+    pad = int(size * 0.06)
+    rect = [pad, pad, size - pad, size - pad]
+    radius = int(size * 0.18)
+
+    # 背景渐变（模拟，用两层半透明）
+    d.rounded_rectangle(rect, radius=radius, fill=(30, 30, 46, 255))
+
+    # 上半部分亮色渐变
+    inner = [pad + 4, pad + 4, size - pad - 4, size // 2]
+    d.rounded_rectangle(inner, radius=radius - 2, fill=(40, 40, 60, 255))
+
+    # 终端窗口
+    tw_margin = int(size * 0.16)
+    tw_top = int(size * 0.20)
+    tw_bottom = int(size * 0.78)
+    tw_left = tw_margin
+    tw_right = size - tw_margin
+    tw_radius = int(size * 0.04)
+
+    # 终端窗口阴影
+    shadow_offset = max(2, size // 64)
+    d.rounded_rectangle(
+        [tw_left + shadow_offset, tw_top + shadow_offset,
+         tw_right + shadow_offset, tw_bottom + shadow_offset],
+        radius=tw_radius, fill=(0, 0, 0, 60)
+    )
+
+    # 终端窗口背景
+    d.rounded_rectangle(
+        [tw_left, tw_top, tw_right, tw_bottom],
+        radius=tw_radius, fill=(12, 12, 20, 255)
+    )
+
+    # 终端标题栏
+    tb_height = int(size * 0.055)
+    d.rounded_rectangle(
+        [tw_left, tw_top, tw_right, tw_top + tb_height],
+        radius=tw_radius, fill=(50, 50, 70, 255)
+    )
+    # 底部直角覆盖（标题栏只有上面圆角）
+    d.rectangle(
+        [tw_left, tw_top + tb_height - tw_radius, tw_right, tw_top + tb_height],
+        fill=(50, 50, 70, 255)
+    )
+
+    # 三个小圆点（macOS 风格窗口按钮）
+    dot_r = max(2, int(size * 0.016))
+    dot_y = tw_top + tb_height // 2
+    dot_start = tw_left + int(size * 0.04)
+    dot_gap = int(size * 0.045)
+    for i, color in enumerate([(239, 83, 80), (255, 167, 38), (102, 187, 106)]):
+        cx = dot_start + i * dot_gap
+        d.ellipse([cx - dot_r, dot_y - dot_r, cx + dot_r, dot_y + dot_r], fill=color)
+
+    # >_ 提示符
+    cx = tw_left + int(size * 0.06)
+    cy = tw_top + tb_height + int(size * 0.10)
+    line_w = max(2, int(size * 0.022))
+    arrow_len = int(size * 0.08)
+    gap = int(size * 0.02)
+
+    # > 符号
+    d.line([cx, cy, cx + arrow_len, cy + arrow_len // 2],
+           fill=(102, 187, 106), width=line_w)
+    d.line([cx, cy + arrow_len, cx + arrow_len, cy + arrow_len // 2],
+           fill=(102, 187, 106), width=line_w)
+
+    # _ 光标
+    cursor_x = cx + arrow_len + gap
+    cursor_w = int(size * 0.06)
+    cursor_h = max(2, int(size * 0.018))
+    d.rounded_rectangle(
+        [cursor_x, cy + arrow_len // 2 - cursor_h // 2,
+         cursor_x + cursor_w, cy + arrow_len // 2 + cursor_h // 2],
+        radius=max(1, cursor_h // 3), fill=(137, 180, 250)
+    )
+
+    # SSH 连接线（底部装饰）
+    line_y = tw_bottom + int(size * 0.05)
+    if line_y < size - pad:
+        # 连接节点
+        node_r = max(2, int(size * 0.012))
+        n1 = (tw_left + int(size * 0.04), line_y)
+        n2 = (tw_right - int(size * 0.04), line_y)
+        d.ellipse([n1[0]-node_r, n1[1]-node_r, n1[0]+node_r, n1[1]+node_r],
+                  fill=(137, 180, 250))
+        d.ellipse([n2[0]-node_r, n2[1]-node_r, n2[0]+node_r, n2[1]+node_r],
+                  fill=(137, 180, 250))
+        d.line([n1[0]+node_r, n1[1], n2[0]-node_r, n2[1]],
+               fill=(137, 180, 250, 160), width=max(1, line_w // 2))
+
+    return img
+
+
+def main():
+    # 生成 256x256 主图
+    icon = draw_icon(SIZE)
+    png_path = os.path.join(OUT_DIR, "icon.png")
+    icon.save(png_path)
+    print(f"Saved {png_path} ({SIZE}x{SIZE})")
+
+    # 生成多尺寸 ICO（Pillow 自动从 256x256 缩放到各尺寸）
+    sizes = [(16, 16), (24, 24), (32, 32), (48, 48), (64, 64), (128, 128), (256, 256)]
+    ico_path = os.path.join(OUT_DIR, "icon.ico")
+    icon.save(ico_path, format="ICO", sizes=sizes)
+    print(f"Saved {ico_path} (sizes: {[s[0] for s in sizes]})")
+    print("Done!")
+
+
+if __name__ == "__main__":
+    main()