Design custom scan excludes in settings

[Muawiya-contact]

Goal

Design and add a small settings surface for scan excludes.

Diskern has default excluded paths like /proc, /sys, and system folders. Advanced users may want to add their own folders that should never be walked.

Why this is advanced

This touches safety and scan authority. A bad design could make a scan silently skip too much or make results confusing.

Current code pointer

Defaults are here:

fn default_excludes() -> Vec<String> {
    let mut v = vec![];
    #[cfg(target_os = "linux")]
    v.extend(["/proc", "/sys", "/dev", "/run"].map(String::from));
    v
}

File:

crates/diskern-core/src/scanner.rs

Suggested approach

Start with a short design comment in the issue or PR before coding:

• where custom excludes are stored
• how the UI explains them
• how a user resets them
• how tests prove excluded scan roots still fail clearly

Acceptance criteria

• Custom excludes are explicit and visible to the user.
• Excluding a chosen scan root still produces a clear error.
• Tests cover at least one custom exclude case.