Fix SSE connection closing prematurely for non-existent rooms

The server was calling exit() immediately when a room didn't exist,
which caused the SSE connection to open and then close right away.
This triggered EventSource to reconnect in a loop.

Now the server keeps the connection open and sends keepalives even
for rooms that don't exist yet. This is the correct SSE behavior -
maintain the connection and stream data when it becomes available.

Fixes the "connection established then immediately errors" issue
seen in diagnostic tests.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

server/php/server.php

@@ -93,23 +93,14 @@ function handleStream() {
         sendError('Missing room name', 400);
     }
 
-    // Passphrase is optional for streaming (read-only)
-    // If room doesn't exist yet, return empty stream
-    if (!roomExists($room)) {
-        // Return empty stream - room doesn't exist yet
-        header('Content-Type: text/event-stream');
-        header('Cache-Control: no-cache');
-        header('X-Accel-Buffering: no');
-        echo ": waiting for room to be created\n\n";
-        flush();
-        exit();
-    }
-
     // Set SSE headers
     header('Content-Type: text/event-stream');
     header('Cache-Control: no-cache');
     header('X-Accel-Buffering: no'); // Disable nginx buffering
 
+    // Passphrase is optional for streaming (read-only)
+    // If room doesn't exist yet, we'll keep the connection open and wait for it
+
     // Track last known count
     $lastCount = 0;