add Twitch identity disconnect controls

src/App.svelte

@@ -328,6 +328,23 @@
     }
   }
 
+  async function revokeOAuth(identity: 'streamer' | 'bot') {
+    oauthBusy = true;
+    oauthError = '';
+    try {
+      const response = await fetch(`${serverAddress}/api/v1/twitch/oauth/revoke?identity=${identity}`, {
+        method: 'POST',
+        headers: { authorization: `Bearer ${sessionToken}` },
+      });
+      if (!response.ok) throw new Error('The server could not revoke this Twitch authorization.');
+      await loadStreamInfo();
+    } catch (error) {
+      oauthError = error instanceof Error ? error.message : 'The Twitch authorization could not be revoked.';
+    } finally {
+      oauthBusy = false;
+    }
+  }
+
   async function copyOAuthLink() {
     if (!oauthLink) return;
     await navigator.clipboard.writeText(oauthLink).catch(() => {
@@ -378,7 +395,9 @@
         {#if authenticated}
           <div class="oauth-actions">
             <button class="secondary-action" onclick={() => createOAuthLink('streamer')} disabled={oauthBusy}>CONNECT STREAMER</button>
+            <button class="secondary-action" onclick={() => revokeOAuth('streamer')} disabled={oauthBusy}>DISCONNECT STREAMER</button>
             <button class="secondary-action" onclick={() => createOAuthLink('bot')} disabled={oauthBusy}>CONNECT BOT</button>
+            <button class="secondary-action" onclick={() => revokeOAuth('bot')} disabled={oauthBusy}>DISCONNECT BOT</button>
           </div>
           {#if oauthLink}
             <div class="oauth-link-card">