feat: initialize markr nostr bookmark client

- Add project structure with TypeScript, React, and Vite
- Implement nostr authentication using browser extension (NIP-07)
- Add NIP-51 compliant bookmark fetching and display
- Create minimal UI with login and bookmark components
- Integrate applesauce-core and applesauce-react libraries
- Add responsive styling with dark/light mode support
- Include comprehensive README with setup instructions

This is a minimal MVP for a nostr bookmark client that allows users to
view their bookmarks according to NIP-51 specification.

node_modules/mdast-util-to-markdown/lib/util/format-heading-as-setext.js

@@ -0,0 +1,34 @@
+/**
+ * @import {State} from 'mdast-util-to-markdown'
+ * @import {Heading} from 'mdast'
+ */
+
+import {EXIT, visit} from 'unist-util-visit'
+import {toString} from 'mdast-util-to-string'
+
+/**
+ * @param {Heading} node
+ * @param {State} state
+ * @returns {boolean}
+ */
+export function formatHeadingAsSetext(node, state) {
+  let literalWithBreak = false
+
+  // Look for literals with a line break.
+  // Note that this also
+  visit(node, function (node) {
+    if (
+      ('value' in node && /\r?\n|\r/.test(node.value)) ||
+      node.type === 'break'
+    ) {
+      literalWithBreak = true
+      return EXIT
+    }
+  })
+
+  return Boolean(
+    (!node.depth || node.depth < 3) &&
+      toString(node) &&
+      (state.options.setext || literalWithBreak)
+  )
+}