ZoiteChat 2.18.0~pre5

This pre-release keeps pushing ZoiteChat toward the 2.18 stable release, with the biggest work centred on preferences/config reliability, GTK3 theming, UI polish, tray stability, and packaging fixes.

Fixes

• Overhauled preferences/config saving: fully staged and transactional, debounced
  with flush on close, write failures now surfaced.
• Overhauled GTK theme handling: live preview, correct colour reset persistence,
  proper file:// import paths, consistent menubar CSS.
• Fixed GTK entry scroll artifact in the input box.
• Hardened tray menu lifetime; fixed stale pointer crash on menu destruction.
• Fixed AppIndicator tray init for Wayland/source builds; skip redundant X11
  tray probe for AppIndicator builds.
• Split topic/mode rows in channel bar, tighten spacing, persist userlist column widths.
• Preserve saved right-pane size on first layout.
• Fixed sounds prefs section.
• Fixed chanview tree layout and header alignment; tighten topic URL hit-testing.
• Dropped realpath() in favour of GLib-only absolute path build.
• Made About dialog links explicit; added GPL licence URL.
• Added licence headers to new source files.
• Windows installer: fixed VC++ redist URL, added non-plugin download fallback,
  switched to registry-based runtime detection.
• Made libayatana-appindicator a required dep in PKGBUILD.
• Cleaned up Meson libperl detection.

Note

This is still a pre-release, so a few rough edges are still being sanded down, especially around GTK theming and general polish.