Add a fixed width font for text

Text placed in different locations on the shield can appear at different sizes due to scaling words of different length. If we had a fixed width font (and made sure the words had the same number of characters, e.g. "Left " and "Right") then text should appear at the same size. Need to find a suitably licenced fixed width font, available as SVG glyphs with hopefully quite a wide character set....

没有指定文件、测试或入口点。首先定位将文本渲染为 shield SVG 的代码，然后研究具有合适许可和 SVG 字形支持的等宽字体。完成标准是选定一个可接受的字体，并确认等长单词以一致的大小进行渲染。

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