chore(gemini): add the initial style guide for suggestions (#260)

.gemini/styleguide.md

@@ -0,0 +1,42 @@
+# Gemini Code Assist Style Guide
+
+## Suggestions
+
+### Core Requirement
+
+**Always wrap code suggestions in GitHub suggestion blocks** to enable one-click application by maintainers.
+
+### Format
+
+Use GitHub's suggestion syntax for all code recommendations:
+
+```suggestion
+// Your suggested code here
+```
+
+### Multiple Options
+
+When offering multiple approaches, provide separate labeled suggestion blocks:
+
+**Option A - Performance focused:**
+
+```suggestion
+function processItems(items) {
+  let result = 0;
+  for (const item of items) {
+    result += item.value;
+  }
+  return result;
+}
+```
+
+**Option B - Functional approach:**
+
+```suggestion
+const processItems = (items) =>
+  items.reduce((sum, item) => sum + item.value, 0);
+```
+
+### That's It
+
+Continue providing your normal comprehensive analysis, explanations, and recommendations. The only change is wrapping code suggestions in suggestion blocks so maintainers can easily apply them.