Feature request: Make default room not mandatory

cargo run -- --login password --credentials . --store .

   Compiling matrix-commander v0.11.0 (/home/ubuntu/matrix-commander-rs)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 18.36s
     Running `target/debug/matrix-commander-rs --login password --credentials . --store .`
Enter your Matrix homeserver (e.g. https://some.homeserver.org): https://matrix.org
Enter your full Matrix username (e.g. @john:some.homeserver.org): @overclock3000:matrix.org
Enter Matrix password for this user: 
Enter your desired name for the Matrix device that is going to be created for you (e.g. matrix-commander-rs): matrix-commander-rs
Enter name of one of your Matrix rooms that you want to use as default room  (e.g. !someRoomId:some.homeserver.org): 
2026-07-04T15:40:32.129299Z ERROR matrix_commander_rs: Error: Empty name of default room is not allowed!
Enter name of one of your Matrix rooms that you want to use as default room  (e.g. !someRoomId:some.homeserver.org): 

Related to #219.