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/__init__.py

@@ -0,0 +1,50 @@
+from flask import Blueprint, render_template, current_app, redirect, url_for, request
+
+blueprint = Blueprint(
+    'matrix_iframe',
+    __name__,
+    template_folder='templates',
+    static_folder='static',
+    static_url_path='/static/matrix_iframe',
+)
+
+
+def init_app(app, server_url='', room_alias='', base_template='layout.html', login_endpoint=None):
+    """
+    Register the Matrix chat blueprint with a Flask app.
+
+    Args:
+        server_url:      Matrix homeserver base URL, e.g. "https://matrix.sticknife.com"
+        room_alias:      Matrix room alias, e.g. "#sticknife-library:matrix.sticknife.com"
+        base_template:   Jinja2 base template to extend, default "layout.html"
+        login_endpoint:  Flask endpoint to redirect unauthenticated users to,
+                         e.g. "web.login". If None, no auth guard is applied.
+    """
+    app.config.setdefault('MATRIX_SERVER_URL', server_url)
+    app.config.setdefault('MATRIX_ROOM_ALIAS', room_alias)
+    app.config.setdefault('MATRIX_CHAT_BASE', base_template)
+    app.config.setdefault('MATRIX_CHAT_LOGIN_ENDPOINT', login_endpoint)
+    app.register_blueprint(blueprint)
+
+
+@blueprint.before_request
+def _auth_guard():
+    login_endpoint = current_app.config.get('MATRIX_CHAT_LOGIN_ENDPOINT')
+    if not login_endpoint:
+        return
+    try:
+        from flask_login import current_user
+        if not current_user.is_authenticated:
+            return redirect(url_for(login_endpoint, next=request.url))
+    except ImportError:
+        pass
+
+
+@blueprint.route('/chat')
+def chat():
+    return render_template(
+        'matrix_iframe/chat.html',
+        matrix_server=current_app.config.get('MATRIX_SERVER_URL', ''),
+        matrix_room_alias=current_app.config.get('MATRIX_ROOM_ALIAS', ''),
+        base_template=current_app.config.get('MATRIX_CHAT_BASE', 'layout.html'),
+    )