fix: exclude .cache/og from watcher to prevent build loop

OG image generation writes to .cache/og/ which the watcher detects
as file changes, triggering another build that runs OG generation
again in an infinite loop.

eleventy.config.js

@@ -42,6 +42,8 @@ export default function (eleventyConfig) {
   eleventyConfig.watchIgnores.add("/app/data/site/**");
   eleventyConfig.watchIgnores.add("_pagefind");
   eleventyConfig.watchIgnores.add("_pagefind/**");
+  eleventyConfig.watchIgnores.add(".cache/og");
+  eleventyConfig.watchIgnores.add(".cache/og/**");
 
   // Configure markdown-it with linkify enabled (auto-convert URLs to links)
   const md = markdownIt({