feat: implement main blueprint with routes for index, profile, and logout

app/blueprints/main.py

@@ -0,0 +1,29 @@
+from flask import Blueprint, render_template
+from flask_dance.contrib.google import google
+from ..auth import login_required
+
+main_bp = Blueprint("main", __name__)
+
+
+@main_bp.route("/")
+@login_required
+def index():
+    return render_template("index.html")
+
+
+@main_bp.route("/profile")
+@login_required
+def profile():
+    resp = google.get("/oauth2/v2/userinfo")
+    assert resp.ok, resp.text
+
+    user_info = resp.json()
+    return render_template("profile.html", user=user_info)
+
+
+@main_bp.route("/logout")
+@login_required
+def logout():
+    from flask import redirect, url_for
+    google.token = None
+    return redirect(url_for('main.index'))