Fix npm audit vulnerabilities and broken image build

Eleventy Image v7 removed its synchronous stats API, which broke the
build. Rather than downgrade (older versions bundle a vulnerable sharp),
adapt to v7 and clear out the remaining vulnerable dependencies:

- Make the `image` shortcode async
- Replace the unmaintained markdown-it-eleventy-img with a local plugin
  that pre-loads image metadata in eleventy.before, so markdown (and
  feed) images keep rendering as <picture> elements
- Upgrade @11ty/eleventy-fetch to v6
- Swap npm-run-all for the maintained npm-run-all2 fork
- Override eleventy-plugin-og-image's satori (and its pinned fflate) to
  patched versions, and set explicit heading weights in the OG template
  so newer satori doesn't synthesise bold text

config/plugins/image.js

@@ -9,15 +9,14 @@ const defaultSizes = `
     (min-width: 2500px) 3840px
 `;
 
-const imageShortcode = (src, alt, cls, sizes = defaultSizes, widths = [300, 600, 1000, 1440, 2500, 3840]) => {
+const imageShortcode = async (src, alt, cls, sizes = defaultSizes, widths = [300, 600, 1000, 1440, 2500, 3840]) => {
     let options = {
         widths: widths,
         formats: ['webp', 'jpeg'],
         outputDir: "./_site/img",
     };
 
-    // generate images, while this is async we don’t wait
-    Image(src, options);
+    let metadata = await Image(src, options);
 
     let imageAttributes = {
         class: cls,
@@ -25,8 +24,6 @@ const imageShortcode = (src, alt, cls, sizes = defaultSizes, widths = [300, 600,
         sizes,
         decoding: "async",
     };
-    // get metadata even the images are not fully generated
-    let metadata = Image.statsSync(src, options);
     return Image.generateHTML(metadata, imageAttributes);
 }
 
@@ -49,6 +46,6 @@ const remoteImageShortcode = async (src, alt, cls, sizes = defaultSizes, widths
       return Image.generateHTML(metadata, imageAttributes);
 }
 export default function(eleventyConfig) {
-	eleventyConfig.addShortcode("image", imageShortcode);
+	eleventyConfig.addAsyncShortcode("image", imageShortcode);
     eleventyConfig.addAsyncShortcode("remoteImage", remoteImageShortcode);
 }