Add initial implementation of Matrix chat widget with Flask blueprint

- Create .gitignore to exclude Python-related files
- Implement chat blueprint in __init__.py
- Add chat HTML template with input and message display
- Create CSS for chat styling
- Develop JavaScript for chat functionality and Matrix API integration
- Configure pyproject.toml for project metadata and dependencies

matrix_iframe/templates/matrix_iframe/chat.html

@@ -0,0 +1,19 @@
+{% extends base_template %}
+
+{% block header %}
+<link rel="stylesheet" href="{{ url_for('matrix_iframe.static', filename='matrix_iframe/matrix-chat.css') }}">
+{% endblock %}
+
+{% block body %}
+<div id="matrix-chat-root"
+     data-matrix-server="{{ matrix_server }}"
+     data-matrix-room="{{ matrix_room_alias }}">
+  <div id="matrix-chat-status" class="matrix-status"></div>
+  <div id="matrix-messages" class="matrix-messages"></div>
+  <div class="matrix-input-bar">
+    <input type="text" id="matrix-input" class="matrix-input" placeholder="Send a message…" autocomplete="off">
+    <button id="matrix-send" class="matrix-send-btn">Send</button>
+  </div>
+</div>
+<script src="{{ url_for('matrix_iframe.static', filename='matrix_iframe/matrix-chat.js') }}"></script>
+{% endblock %}