Add /auth/clear endpoint to reset session cookies

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infrastructure/oauth.py

@@ -120,6 +120,16 @@ def create_oauth_blueprint(app_name: str) -> Blueprint:
 
         return redirect(next_url, 303)
 
+    @bp.get("/clear")
+    @bp.get("/clear/")
+    async def clear():
+        """One-time migration helper: clear all session cookies."""
+        qsession.clear()
+        resp = redirect("/")
+        resp.delete_cookie("blog_session", domain=".rose-ash.com", path="/")
+        resp.delete_cookie("sso_hint", domain=".rose-ash.com", path="/")
+        return resp
+
     @bp.post("/logout")
     @bp.post("/logout/")
     async def logout():