Visualizer mode set with 'v' is not persisted across restarts

[pythrick]

When I cycle visualizer mode with v, it changes in the current session but resets to default after restart.

Repro:

1. Start cliamp
2. Press v a few times (for example to Wave)
3. Quit
4. Start cliamp again

Expected:

• last selected visualizer mode is loaded on startup

Actual:

• startup falls back to default visualizer

I tracked this down locally: the v handler updates m.vis.Mode but doesn't save visualizer to config, while repeat and shuffle do persist right away.

I can open a small PR for this.