feat: Add GitHub link float menu button

app/components/float-menu.tsx

@@ -0,0 +1,39 @@
+"use client"
+
+import { Github } from "lucide-react"
+import { Button } from "@/components/ui/button"
+import {
+  Tooltip,
+  TooltipContent,
+  TooltipProvider,
+  TooltipTrigger,
+} from "@/components/ui/tooltip"
+
+export function FloatMenu() {
+  return (
+    <div className="fixed bottom-6 right-6">
+      <TooltipProvider>
+        <Tooltip>
+          <TooltipTrigger asChild>
+            <Button
+              variant="outline"
+              size="icon"
+              className="bg-white dark:bg-background rounded-full shadow-lg group relative border-primary/20"
+              onClick={() => window.open("https://github.com/beilunyang/moemail", "_blank")}
+            >
+              <Github 
+                className="w-4 h-4 transition-all duration-300 text-primary group-hover:scale-110"
+              />
+              <span className="sr-only">获取网站源代码</span>
+            </Button>
+          </TooltipTrigger>
+          <TooltipContent>
+            <div className="text-sm">
+              <p>获取网站源代码</p>
+            </div>
+          </TooltipContent>
+        </Tooltip>
+      </TooltipProvider>
+    </div>
+  )
+}