feat(system): 添加设备信息及重启关机控制

关于页展示宿主系统、处理器、架构、内核和资源占用，合并同一文件系统上的系统与 MSD 容量。
新增 Linux 宿主机重启和关机接口，在其他设置中提供二次确认、请求互斥及失败提示。
修正 Linux 磁盘已用空间计算，并补充设备信息和电源控制的后端单元测试。

验证：独立暂存快照前端构建通过；6 项后端测试通过；设置页保存、系统信息及模拟电源控制浏览器测试通过。

src/diagnostics/host.rs

@@ -0,0 +1,143 @@
+//! Read-only host metadata and filesystem identity for the About page.
+use super::{get_disk_space, DiskSpaceInfo};
+use serde::Serialize;
+use std::path::{Path, PathBuf};
+
+#[derive(Debug, Serialize)]
+pub struct HostInfo {
+    pub operating_system: String,
+    pub architecture: &'static str,
+    pub kernel: Option<String>,
+    pub cpu_count: usize,
+    pub storage: StorageInfo,
+}
+
+#[derive(Debug, Serialize)]
+pub struct StorageInfo {
+    pub system: Option<DiskSpaceInfo>,
+    pub msd: Option<DiskSpaceInfo>,
+    /// Unknown identity must never be interpreted as a shared filesystem.
+    pub shared_partition: Option<bool>,
+}
+
+pub fn get_host_info(msd_path: &Path) -> HostInfo {
+    let operating_system = std::fs::read_to_string("/etc/os-release")
+        .ok()
+        .and_then(|text| os_release_name(&text))
+        .unwrap_or_else(|| std::env::consts::OS.to_string());
+    let kernel = std::fs::read_to_string("/proc/sys/kernel/osrelease")
+        .ok()
+        .map(|value| value.trim().to_string())
+        .filter(|value| !value.is_empty());
+    HostInfo {
+        operating_system,
+        architecture: std::env::consts::ARCH,
+        kernel,
+        cpu_count: std::thread::available_parallelism()
+            .map(usize::from)
+            .unwrap_or(1),
+        storage: storage_info(system_root().as_path(), msd_path),
+    }
+}
+
+fn system_root() -> PathBuf {
+    #[cfg(windows)]
+    {
+        PathBuf::from(std::env::var_os("SystemDrive").unwrap_or_else(|| "C:".into())).join("\\")
+    }
+    #[cfg(not(windows))]
+    {
+        PathBuf::from("/")
+    }
+}
+
+fn os_release_name(text: &str) -> Option<String> {
+    text.lines().find_map(|line| {
+        let value = line
+            .strip_prefix("PRETTY_NAME=")?
+            .trim()
+            .trim_matches(['\'', '"']);
+        (!value.is_empty()).then(|| value.to_string())
+    })
+}
+
+// MSD directories may not have been created yet. Read their containing filesystem
+// without creating directories or changing permissions.
+fn existing_ancestor(path: &Path) -> Option<PathBuf> {
+    if path.as_os_str().is_empty() {
+        return None;
+    }
+    let mut candidate = if path.is_absolute() {
+        path.to_path_buf()
+    } else {
+        std::env::current_dir().ok()?.join(path)
+    };
+    loop {
+        match std::fs::metadata(&candidate) {
+            Ok(_) => return Some(candidate),
+            Err(error) if error.kind() == std::io::ErrorKind::NotFound => {
+                if !candidate.pop() {
+                    return None;
+                }
+            }
+            Err(_) => return None,
+        }
+    }
+}
+
+fn storage_info(system: &Path, msd: &Path) -> StorageInfo {
+    let system = existing_ancestor(system);
+    let msd = existing_ancestor(msd);
+    StorageInfo {
+        system: system.as_deref().and_then(|path| get_disk_space(path).ok()),
+        msd: msd.as_deref().and_then(|path| get_disk_space(path).ok()),
+        shared_partition: system
+            .as_deref()
+            .zip(msd.as_deref())
+            .and_then(|(a, b)| same_filesystem(a, b)),
+    }
+}
+
+#[cfg(unix)]
+fn same_filesystem(a: &Path, b: &Path) -> Option<bool> {
+    use std::os::unix::fs::MetadataExt;
+    Some(std::fs::metadata(a).ok()?.dev() == std::fs::metadata(b).ok()?.dev())
+}
+
+#[cfg(not(unix))]
+fn same_filesystem(_a: &Path, _b: &Path) -> Option<bool> {
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn distribution_name_handles_quotes_and_missing_values() {
+        assert_eq!(
+            os_release_name("NAME=Linux\nPRETTY_NAME=\"OpenWrt 24.10\"\n"),
+            Some("OpenWrt 24.10".into())
+        );
+        assert_eq!(os_release_name("PRETTY_NAME=\n"), None);
+        assert_eq!(os_release_name("NAME=Linux\n"), None);
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn nested_msd_directory_shares_its_existing_parent_filesystem() {
+        let parent = tempfile::tempdir().unwrap();
+        let missing = parent.path().join("not-created/msd");
+        let storage = storage_info(parent.path(), &missing);
+        assert_eq!(storage.shared_partition, Some(true));
+        assert!(storage.system.is_some() && storage.msd.is_some());
+        assert!(!missing.exists());
+    }
+
+    #[test]
+    fn missing_msd_is_not_a_duplicate_system_partition() {
+        let storage = storage_info(&system_root(), Path::new(""));
+        assert!(storage.msd.is_none());
+        assert_eq!(storage.shared_partition, None);
+    }
+}