Automate NetworkManager management and Secret Agent startup for minimal Debian installs

### Feature Description

I'd love to see DMS automatically handle a few "quality of life" configurations when it detects a minimal Debian install (without a full DE). Currently, a fresh install on Debian leaves the network "unmanaged" and the keyring inactive, which breaks the DMS Network UI and VPNs like Proton.

Specific changes to automate:

NetworkManager Config: Automatically set managed=true in /etc/NetworkManager/NetworkManager.conf. Currently, it defaults to false, making Ethernet invisible in the DMS settings

Keyring Autostart: Ensure gnome-keyring-daemon --start --components=secrets is triggered. Without this, the Network UI is blank/broken and cannot save passwords

### Use Case

This would be a lifesaver for anyone coming from Arch or doing a "netinst" of Debian! Right now, if you just install Niri + DMS, your Ethernet shows as "Disconnected" even if you're online. Automating these small tweaks would make the "out-of-the-box" experience feel way more polished especially for broke college students who just want their stuff to work without diving into terminal configs for an hour.

### Compositor(s)

Niri

### If Other, please specify

_No response_

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_