Add comprehensive AppImage metadata extraction, display, and bug fixes

- Add AppStream XML parser (quick-xml) to extract rich metadata from bundled
  metainfo/appdata files: description, developer, license, URLs, keywords,
  categories, content rating, release history, and MIME types
- Database migration v9: 16 new columns for extended metadata storage
- Extended inspector to parse AppStream XML, desktop entry extended fields,
  and detect binary signatures without executing AppImages
- Redesigned detail view overview tab with 8 conditional groups: About,
  Description, Links, Release History, Usage, Capabilities, File Info
- Fix crash on exit caused by stale GLib SourceId removal in debounce timers
- Fix wayland.rs executing AppImages directly to detect squashfs offset,
  replaced with safe binary scan via find_squashfs_offset_for()
- Fix scan skipping re-analysis of apps missing new metadata fields

Cargo.toml

@@ -42,6 +42,9 @@ env_logger = "0.11"
 # Temp directories (for AppImage extraction)
 tempfile = "3"
 
+# XML parsing (for AppStream metainfo)
+quick-xml = "0.37"
+
 # Desktop notifications
 notify-rust = "4"