fix(installer): make the Linux half of Phase 2 compile

Three faults in code that only compiles under cfg(unix), none of which the
Windows build could see:

- `run(...).map(...) == Ok(true)` compared two `Result<_, anyhow::Error>`
  values, and anyhow::Error is not PartialEq. Replaced with `is_ok_and`.
- `command_line` is used only by the Windows registration path, so importing it
  unconditionally is an unused-import error under `-D warnings`. Qualified at
  its call site instead.
- A cfg(not(windows)) assertion block had ended up in the wrong test, leaving it
  referencing a binding from its original one.

Caught by running the same gates the CI runner does inside a rust:1-slim
container against this working tree — fmt, clippy --all-targets -D warnings, and
cargo test --locked all pass there now, as they do on Windows.

Co-Authored-By: Claude <noreply@anthropic.com>

src/service.rs

@@ -31,7 +31,9 @@ use std::path::{Path, PathBuf};
 
 use anyhow::{Context, Result};
 
-use crate::util::{command_line, run, run_ok};
+// `command_line` is used only by the Windows registration path, so it is qualified at its call
+// site rather than imported here — an unconditional import is an unused-import error on Linux.
+use crate::util::{run, run_ok};
 
 /// The unit file name, and the systemd service name with its suffix.
 pub const SYSTEMD_UNIT: &str = "runicgateway-link.service";
@@ -149,7 +151,7 @@ fn prepare_platform() -> Prepared {
 /// Creates the dedicated system user if it is not already there. Returns whether it created it.
 #[cfg(unix)]
 fn ensure_user(user: &str) -> Result<bool> {
-    if run("id", &["-u", user]).map(|o| o.status.success()) == Ok(true) {
+    if run("id", &["-u", user]).is_ok_and(|o| o.status.success()) {
         return Ok(false);
     }
     // `useradd` is the near-universal spelling; `adduser` is the fallback for Debian's wrapper and
@@ -373,7 +375,7 @@ fn register_windows(binary: &Path, config: &Path, restart: bool) -> Result<Outco
         anyhow::bail!(
             "`{}` failed with exit code {}. Check the Windows event log; a service that exits \
              immediately usually cannot read its config: {}",
-            command_line("sc.exe", &["start", WINDOWS_SERVICE]),
+            crate::util::command_line("sc.exe", &["start", WINDOWS_SERVICE]),
             start.status.code().unwrap_or(-1),
             config.display()
         );
@@ -798,6 +800,16 @@ mod tests {
             // The write grant belongs to the database directory, which is not always the config's.
             assert!(steps.contains("/var/lib/runicgateway'"), "{steps}");
         }
+        #[cfg(not(windows))]
+        {
+            assert!(steps.contains("systemctl enable --now"), "{steps}");
+            assert!(
+                steps.contains("ExecStart=/usr/bin/runicgateway-link"),
+                "{steps}"
+            );
+            // Non-systemd hosts get the requirements, not just a unit they cannot use.
+            assert!(steps.contains("without systemd"), "{steps}");
+        }
     }
 
     #[test]
@@ -826,16 +838,6 @@ mod tests {
             assert_eq!(protected, unprotected);
             assert!(protected.contains("chown runicgateway"), "{protected}");
         }
-        #[cfg(not(windows))]
-        {
-            assert!(steps.contains("systemctl enable --now"), "{steps}");
-            assert!(
-                steps.contains("ExecStart=/usr/bin/runicgateway-link"),
-                "{steps}"
-            );
-            // Non-systemd hosts get the requirements, not just a unit they cannot use.
-            assert!(steps.contains("without systemd"), "{steps}");
-        }
     }
 
     #[test]