Less verbose logging options

**is your feature request related to a problem? Please describe.**

By default logs are kind of all or nothing setup. With `-q` nothing is logged including stuff like user bans. (thus making `thank you for playing (see fileserver log and readme)` not helpful at all)

I tried to limit some logs with very wide `--lf-url`, but this only stops logging web requests. Entering a directory with images still generates a ton of thumbnail generating logs for example. This makes it quite hard to actually find useful logs when troubleshooting.

**Describe the idea / solution you'd like**

Global log level would be nice. At the very least implement this for the most "noisy" logs like access log and thumbnails. It would be nice if only failures were logged for these for example.

**Describe any alternatives you've considered**

I'm using `-q` right now, but that one is a bit too much, I would not mind some startup logs and such. I also appreciate some warning messages. The `--lf-url` can limit the access logs, but as far as I can tell this will also prevent failed access logs.

Look at the logging setup in copyparty, likely in the main server module or a dedicated logging configuration. Identify where access logs and thumbnail generation logs are emitted. The goal is to add a global log level or separate controls for noisy components, ensuring failures are still logged. Check existing flags like `-q` and `--lf-url` to understand the current logging structure.

Written by the indexing model from the issue text.