Cloud-first UX: default to Deepgram, gate start button, add room sharing

- Change default transcription mode from local to byok (cloud/Deepgram)
- Move Transcription Mode selector to top of settings for visibility
- Hide local-only settings (model, VAD, timing) when cloud mode selected
- Disable Start button until API key (byok) or login (managed) is configured
- Add room creation and share code flow to Shared Captions section
- Add POST /api/create-room endpoint to Node.js sync server
- Update default sync URL placeholder to caption.shadowdao.com

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/nodejs/server.js

@@ -703,6 +703,36 @@ app.post('/api/send', async (req, res) => {
     }
 });
 
+// Create room explicitly (no transcription needed)
+app.post('/api/create-room', async (req, res) => {
+    try {
+        const { room, passphrase } = req.body;
+
+        if (!room || !passphrase) {
+            return res.status(400).json({ error: 'Missing room or passphrase' });
+        }
+
+        // Check if room already exists
+        const existing = await loadRoom(room);
+        if (existing) {
+            const valid = await verifyPassphrase(room, passphrase);
+            if (!valid) {
+                return res.status(401).json({ error: 'Room exists with different passphrase' });
+            }
+            return res.json({ status: 'ok', room, created: false, message: 'Room already exists' });
+        }
+
+        // Create the room (verifyPassphrase creates it if it doesn't exist)
+        await verifyPassphrase(room, passphrase);
+
+        console.log(`[Room] Created room "${room}"`);
+        res.json({ status: 'ok', room, created: true });
+    } catch (err) {
+        console.error('Error in /api/create-room:', err);
+        res.status(500).json({ error: err.message });
+    }
+});
+
 // List transcriptions
 app.get('/api/list', async (req, res) => {
     try {