markdown: math set by KaTeX, fetched only when a page has some

$x^2$ inline, $$…$$ for display, and a ```math block, the way GitHub
writes them, in documents, shared pages and .md files alike. KaTeX loads
on first use; until then the math shows as its source. Only the woff2
fonts are bundled.

web/bun.lock

@@ -15,6 +15,7 @@
         "@lezer/highlight": "^1.2.1",
         "@replit/codemirror-vim": "^6.2.1",
         "dompurify": "^3.2.4",
+        "katex": "^0.19.0",
         "marked": "^15.0.6",
       },
       "devDependencies": {
@@ -212,6 +213,8 @@
 
     "clsx": ["clsx@2.1.1", "", {}, "sha512-eYm0QWBtUrBWZWG0d386OGAw16Z995PiOVo2B7bjWSbHedGl5e0ZWaq65kOGgUSNesEIDkB9ISbTg/JK9dhCZA=="],
 
+    "commander": ["commander@15.0.0", "", {}, "sha512-z67u4ZhzCL/Tydu1lJARtEZYWbWaN7oYLHbsuzocr6y4N6WZAagG3RQ4FW61V1/0+jImpj293XfrcYnd1qxtPg=="],
+
     "crelt": ["crelt@1.0.7", "", {}, "sha512-aK6BbWfhf4U/wCcLHKPJl/xa6VkVstRaPywWtMKGwuOLc/wZTyQYuoxgvZnNsBvv7Kg3YTBQYYBCggcviQczuA=="],
 
     "debug": ["debug@4.4.3", "", { "dependencies": { "ms": "^2.1.3" } }, "sha512-RGwwWnwQvkVfavKVt22FGLw+xYSdzARwm0ru6DhTVA3umU5hZc28V3kO4stgYryrTlLpuvgI9GiijltAjNbcqA=="],
@@ -234,6 +237,8 @@
 
     "is-reference": ["is-reference@3.0.3", "", { "dependencies": { "@types/estree": "^1.0.6" } }, "sha512-ixkJoqQvAP88E6wLydLGGqCJsrFUnqoH6HnaczB8XmDH1oaWU+xxdptvikTgaEhtZ53Ky6YXiBuUI2WXLMCwjw=="],
 
+    "katex": ["katex@0.19.0", "", { "dependencies": { "commander": "^15.0.0" }, "bin": { "katex": "cli.js" } }, "sha512-v6Tznz3zJ7u3niRCoDTsumM2+HA2XXcCu+WAacCeHD2z3p9A9Ks987o5FzfTGBN0e8A0vjEgIDvLbICrXpdw/Q=="],
+
     "kleur": ["kleur@4.1.5", "", {}, "sha512-o+NO+8WrRiQEE4/7nwRJhN1HWpVmJm511pBHUxPLtp0BUISzlBplORYSmTclCnJvQq2tKu/sgl3xVpkc7ZWuQQ=="],
 
     "locate-character": ["locate-character@3.0.0", "", {}, "sha512-SW13ws7BjaeJ6p7Q6CO2nchbYEc3X3J6WrmTTDto7yMPqVSZTUyY5Tjbid+Ab8gLnATtygYtiDIJGQRRn2ZOiA=="],