fix: handle intentional logout to trigger immediate observer promotion

When a user explicitly logs out via the logout button, the session should
be removed immediately without grace period, allowing observers to be
promoted right away instead of waiting for the grace period to expire.

Changes:
- Close WebRTC connection immediately on logout
- Clear grace period marker for intentional logout detection
- Add logging to track logout vs disconnect differentiation

This complements the accidental disconnect handling which uses grace period.

web.go

@@ -488,10 +488,30 @@ func handleLogin(c *gin.Context) {
 }
 
 func handleLogout(c *gin.Context) {
-	// Only clear the cookies for this session, don't invalidate the token
+	// Get session ID from cookie before clearing
+	sessionID, _ := c.Cookie("sessionId")
+
+	// Close the WebRTC session immediately for intentional logout
+	if sessionID != "" {
+		if session := sessionManager.GetSession(sessionID); session != nil {
+			websocketLogger.Info().
+				Str("sessionID", sessionID).
+				Msg("Closing session due to intentional logout - no grace period")
+
+			// Close peer connection (will trigger cleanupSession)
+			if session.peerConnection != nil {
+				_ = session.peerConnection.Close()
+			}
+
+			// Clear grace period for intentional logout - observer should be promoted immediately
+			sessionManager.ClearGracePeriod(sessionID)
+		}
+	}
+
+	// Clear the cookies for this session, don't invalidate the token
 	// The token should remain valid for other sessions
 	c.SetCookie("authToken", "", -1, "/", "", false, true)
-	c.SetCookie("sessionId", "", -1, "/", "", false, true) // Clear session ID cookie too
+	c.SetCookie("sessionId", "", -1, "/", "", false, true)
 	c.JSON(http.StatusOK, gin.H{"message": "Logout successful"})
 }