Add Phase 5 enhancements: security, i18n, analysis, backup, notifications

- Database v8 migration: tags, pinned, avg_startup_ms columns
- Security scanning with CVE matching and batch scan
- Bundled library extraction and vulnerability reports
- Desktop notification system for security alerts
- Backup/restore system for AppImage configurations
- i18n framework with gettext support
- Runtime analysis and Wayland compatibility detection
- AppStream metadata and Flatpak-style build support
- File watcher module for live directory monitoring
- Preferences panel with GSettings integration
- CLI interface for headless operation
- Detail view: tabbed layout with ViewSwitcher in title bar,
  health score, sandbox controls, changelog links
- Library view: sort dropdown, context menu enhancements
- Dashboard: system status, disk usage, launch history
- Security report page with scan and export
- Packaging: meson build, PKGBUILD, metainfo

src/core/discovery.rs

@@ -48,7 +48,7 @@ pub fn expand_tilde(path: &str) -> PathBuf {
 /// ELF magic at offset 0: 0x7F 'E' 'L' 'F'
 /// AppImage Type 2 at offset 8: 'A' 'I' 0x02
 /// AppImage Type 1 at offset 8: 'A' 'I' 0x01
-fn detect_appimage(path: &Path) -> Option<AppImageType> {
+pub fn detect_appimage(path: &Path) -> Option<AppImageType> {
     let mut file = File::open(path).ok()?;
     let mut header = [0u8; 16];
     file.read_exact(&mut header).ok()?;
@@ -153,6 +153,15 @@ pub fn scan_directories(dirs: &[String]) -> Vec<DiscoveredAppImage> {
     results
 }
 
+/// Compute the SHA-256 hash of a file, returned as a lowercase hex string.
+pub fn compute_sha256(path: &Path) -> std::io::Result<String> {
+    use sha2::{Digest, Sha256};
+    let mut file = File::open(path)?;
+    let mut hasher = Sha256::new();
+    std::io::copy(&mut file, &mut hasher)?;
+    Ok(format!("{:x}", hasher.finalize()))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;