Add Gemini Code Assist config file (#462)

This configures Gemini Code Assist to be a little bit less noisy and
verbose. Based on experiences with other repos, I find this makes Gemini
more useful.

Author: mhucka

.gemini/config.yaml

@@ -0,0 +1,28 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Summary: configure Gemini Code Assist (https://codeassist.google/).
+# See https://github.com/marketplace/gemini-code-assist for more info.
+
+have_fun: false
+code_review:
+  disable: false
+  comment_severity_threshold: HIGH
+  max_review_comments: -1
+  pull_request_opened:
+    help: false
+    summary: false
+    code_review: true
+    include_drafts: false
+ignore_patterns: []