refactor: remove blog and markdown test pages, update navigation links

- Deleted blog.html and associated blog post files (markdown-test, testddd, node-graphs, welcome).
- Updated index.html to use dynamic navigation links from navLinks.js.
- Enhanced MarkdownRenderer to include new heading pin elements.
- Implemented SVG bezier splines for blog post navigation.
- Adjusted CSS styles for blog layout and new elements.

tools/navLinks.js

@@ -0,0 +1,32 @@
+'use strict';
+
+/**
+ * @typedef {Object} NavLink
+ * @property {string} label
+ * @property {string} href
+ * @property {boolean} [external]
+ */
+
+/** @type {NavLink[]} */
+const NAV_LINKS = [
+    { label: 'blog',      href: '/blog.html' },
+    { label: 'docs',      href: '/docs/' },
+    { label: 'github',    href: 'https://github.com/litruv',               external: true },
+    { label: 'bluesky',   href: 'https://bsky.app/profile/lit.mates.dev',  external: true },
+    { label: 'materials', href: '/materials' },
+];
+
+/**
+ * Renders nav link `<a>` elements as an HTML string.
+ *
+ * @param {string} [indent='  '] - Leading whitespace for each line.
+ * @returns {string}
+ */
+function renderNavLinkItems(indent = '  ') {
+    return NAV_LINKS.map(({ label, href, external }) => {
+        const attrs = external ? ' target="_blank" rel="noopener"' : '';
+        return `${indent}<a href="${href}"${attrs} class="quick-link">${label}</a>`;
+    }).join('\n');
+}
+
+module.exports = { NAV_LINKS, renderNavLinkItems };