chore(fonts): 字体二进制不入库，改用脚本生成

- 远程仓库对单次推送体积有限制，6.7 MB 字体无法一次推送，先从版本库移除
- 新增 tools/build-fonts.py：下载官方分包、合并并子集化，一条命令重建
- @font-face 保留，字体缺失时回退系统字体；离线用例改为按可用性断言

tools/build-fonts.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+"""重新生成界面字体（字体二进制不入库）。
+
+用法：
+    uv run --with fonttools --with brotli tools/build-fonts.py
+
+流程：从 lxgw-wenkai-webfont 的 CDN 下载 Regular / Bold 的全部分包 woff2 子集，
+合并成单个字体后裁剪到 GB2312 + Latin + 中文标点，写入 frontend/public/fonts/。
+生成的字体仅供本地构建与打包使用，不提交到仓库。
+"""
+
+from __future__ import annotations
+
+import io
+import re
+import sys
+import tempfile
+import urllib.request
+from pathlib import Path
+
+try:
+    from fontTools.merge import Merger
+    from fontTools.subset import Options, Subsetter
+    from fontTools.ttLib import TTFont
+except ImportError:  # pragma: no cover - 由 uv --with 保证
+    sys.exit("缺少依赖：uv run --with fonttools --with brotli tools/build-fonts.py")
+
+CDN = "https://cdn.staticfile.net/lxgw-wenkai-webfont/1.7.0/"
+WEIGHTS = {
+    "Regular": "lxgwwenkai-regular.css",
+    "Bold": "lxgwwenkai-bold.css",
+}
+OUT_DIR = Path(__file__).resolve().parent.parent / "frontend" / "public" / "fonts"
+
+
+def fetch(url: str) -> bytes:
+    request = urllib.request.Request(
+        url, headers={"User-Agent": "taskpilot-font-builder"}
+    )
+    with urllib.request.urlopen(request, timeout=60) as response:
+        return response.read()
+
+
+def subset_urls(css_name: str) -> list[str]:
+    css = fetch(CDN + css_name).decode("utf-8")
+    # 形如：src: url('./files/lxgwwenkai-regular-subset-4.woff2')
+    matches = re.findall(r"url\(\s*['\"]?([^'\")]+\.woff2)['\"]?\s*\)", css)
+    urls = sorted({match.lstrip("./") for match in matches})
+    if not urls:
+        raise RuntimeError(f"未能从 {css_name} 解析出字体子集，CDN 格式可能已变更")
+    return urls
+
+
+def build_codepoints() -> set[int]:
+    points: set[int] = set()
+    for start, end in (
+        (0x20, 0x7F),  # ASCII
+        (0xA0, 0x100),  # Latin-1
+        (0x2000, 0x2070),  # 通用标点
+        (0x25A0, 0x2600),  # 几何图形
+        (0x3000, 0x3040),  # 中文标点
+        (0xFF00, 0xFFF0),  # 全角字符
+    ):
+        points.update(range(start, end))
+    points.update(
+        [0x00D7, 0x00F7, 0x2190, 0x2191, 0x2192, 0x2193, 0x2713, 0x2717, 0x23F3]
+    )
+    # GB2312 汉字与符号行
+    for high in range(0xA1, 0xF8):
+        for low in range(0xA1, 0xFF):
+            try:
+                points.add(ord(bytes([high, low]).decode("gb2312")))
+            except UnicodeDecodeError:
+                continue
+    return points
+
+
+def build(weight: str, css_name: str, points: set[int], workdir: Path) -> None:
+    urls = subset_urls(css_name)
+    print(f"[{weight}] 下载 {len(urls)} 个子集…")
+    paths: list[str] = []
+    for url in urls:
+        data = fetch(CDN + url)
+        font = TTFont(io.BytesIO(data))
+        target = workdir / Path(url).name.replace(".woff2", ".ttf")
+        font.save(target)
+        font.close()
+        paths.append(str(target))
+
+    print(f"[{weight}] 合并 {len(paths)} 个字体…")
+    merged = Merger().merge(paths)
+
+    options = Options()
+    options.flavor = "woff2"
+    options.hinting = False
+    options.layout_features = ["*"]
+    options.name_IDs = ["*"]
+    subsetter = Subsetter(options=options)
+    subsetter.populate(unicodes=points)
+    subsetter.subset(merged)
+
+    output = OUT_DIR / f"LXGWWenKai-{weight}.woff2"
+    merged.save(output)
+    print(f"[{weight}] 写出 {output}  {output.stat().st_size / 1024 / 1024:.2f} MB")
+
+
+def main() -> int:
+    OUT_DIR.mkdir(parents=True, exist_ok=True)
+    points = build_codepoints()
+    print(f"目标字符集：{len(points)} 个码位")
+    with tempfile.TemporaryDirectory() as directory:
+        workdir = Path(directory)
+        for weight, css_name in WEIGHTS.items():
+            build(weight, css_name, points, workdir)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())