fix(showcase): allow microphone in demo iframe so voice demos work

The shell embeds each demo in a cross-origin iframe whose `allow`
attribute only granted clipboard access. Browsers block
`getUserMedia({ audio: true })` at the Permissions Policy layer in
cross-origin frames unless the parent grants `microphone` via `allow`,
so every voice demo across every integration threw "Microphone
permission denied" before any user prompt was shown.

Add `microphone` to the iframe `allow` in all three places that embed
demo previews — the per-demo viewer, the standalone preview route, and
the demo drawer — so voice demos work uniformly across all 18
integrations. No other demo type uses getUserMedia / getDisplayMedia
/ geolocation, so no other Permissions Policy features are needed.

Author: AlemTuzlak

showcase/shell/src/app/integrations/[slug]/[demo]/page.tsx

@@ -115,7 +115,7 @@ export default function DemoViewerPage() {
               src={iframeSrc}
               className="h-full w-full border-0 rounded-xl"
               title={`${demo.name} demo`}
-              allow="clipboard-read; clipboard-write"
+              allow="clipboard-read; clipboard-write; microphone"
               sandbox="allow-scripts allow-same-origin allow-forms allow-popups"
             />
           ) : (

showcase/shell/src/app/integrations/[slug]/[demo]/preview/page.tsx

@@ -70,7 +70,7 @@ export default function StandalonePreviewPage() {
         src={src}
         className="h-full w-full border-0"
         title={`${integration.name} — ${demo.name}`}
-        allow="clipboard-read; clipboard-write"
+        allow="clipboard-read; clipboard-write; microphone"
         sandbox="allow-scripts allow-same-origin allow-forms allow-popups"
       />
     </div>

showcase/shell/src/components/demo-drawer.tsx

@@ -203,7 +203,7 @@ export function DemoDrawer({
               src={iframeSrc}
               className="h-full w-full border-0"
               title={`${demoName} demo`}
-              allow="clipboard-read; clipboard-write"
+              allow="clipboard-read; clipboard-write; microphone"
               sandbox="allow-scripts allow-same-origin allow-forms allow-popups"
             />
           )}