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/markdown.js

@@ -9,12 +9,29 @@ import { full as markdownItEmoji } from 'markdown-it-emoji';
 import markdownItFootnote from 'markdown-it-footnote';
 import markdownitMark from 'markdown-it-mark';
 import markdownitAbbr from 'markdown-it-abbr';
-import markdownItEleventyImg from 'markdown-it-eleventy-img';
 import markdownItCallouts from 'markdown-it-obsidian-callouts';
 import { slugifyString } from '../utils.js';
+import { createMarkdownImages } from './markdown-it-image.js';
 
 const icons = JSON.parse(fs.readFileSync('./config/plugins/icons.json'), 'utf-8');
 
+const markdownImages = createMarkdownImages({
+	imageDir: path.join("src", "images"),
+	imgOptions: {
+		widths: [300, 600, 1000, 1440],
+		urlPath: "/img/",
+		outputDir: path.join("_site", "img"),
+		formats: ["avif", "webp", "jpeg"]
+	},
+	globalAttributes: {
+		sizes: `(max-width: 300px) 300px,
+		(max-width: 600px) 600px,
+		(max-width: 1000px) 1000px,
+		(max-width: 1440px) 1440px,
+		100%`
+	}
+});
+
 const markdownLib = markdownIt({
 	html: true,
 	breaks: true,
@@ -53,27 +70,14 @@ const markdownLib = markdownIt({
 	.use(markdownitMark)
 	.use(markdownitAbbr)
 	.use(markdownItCallouts)
-	.use(markdownItEleventyImg, {
-		imgOptions: {
-			widths: [300, 600, 1000, 1440],
-			urlPath: "/img/",
-			outputDir: path.join("_site", "img"),
-			formats: ["avif", "webp", "jpeg"]
-		},
-		globalAttributes: {
-			sizes: `(max-width: 300px) 300px,
-			(max-width: 600px) 600px,
-			(max-width: 1000px) 1000px,
-			(max-width: 1440px) 1440px,
-			100%`
-		}
-	});
+	.use(markdownImages.markdownItPlugin);
 
 markdownLib.renderer.rules.emoji = function(token, idx) {
 	return `<span class="fa-li"><i class="fa-solid fa-${token[idx].markup}" aria-hidden="true"></i></span>`;
 };
 
 export default function(eleventyConfig) {
+	eleventyConfig.addPlugin(markdownImages.eleventyPlugin);
 	eleventyConfig.addFilter('md', content => content ? markdownLib.render(content) : "");
 	eleventyConfig.setLibrary('md', markdownLib);
 }