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/encode-character-reference.js

@@ -0,0 +1,11 @@
+/**
+ * Encode a code point as a character reference.
+ *
+ * @param {number} code
+ *   Code point to encode.
+ * @returns {string}
+ *   Encoded character reference.
+ */
+export function encodeCharacterReference(code) {
+  return '&#x' + code.toString(16).toUpperCase() + ';'
+}