feat(dist): generate completions, editor syntax, man pages, translations

Ports Ghostty's build-data helpers (main_build_data.zig, src/extra/*,
build/mdgen) as the ghostty-build-data binary: bash/zsh/fish
completions, Vim syntax/ftdetect/ftplugin/compiler, Sublime syntax (also
used by bat), terminfo source and ghostty(1)/ghostty(5) markdown. With
the version set to the installed 1.3.1-arch2, all generated files are
byte-identical to the installed Ghostty's.

- `just docs` renders man pages and HTML with pandoc.
- po/: Ghostty's 29 translation catalogs; `just locales` compiles them
  into the com.mitchellh.ghostty gettext domain.
- `just install PREFIX FLATPAK SYSTEM_PACKAGE` installs everything incl.
  terminfo text/termcap outputs and mirrors GhosttyResources.zig install
  modes (Flatpak D-Bus template without systemd; lib/systemd/user for
  system packages).
- Build metadata (version, tip/stable channel, commit, build mode) is
  derived at build time like build_config.zig; GTK/libadwaita
  compile-time versions come from pkg-config instead of constants.

Test Plan:
- cargo run -p ghostty-build-data -- +bash | diff - \
  /usr/share/bash-completion/completions/ghostty (same for zsh/fish/vim)
- just install /tmp/prefix

crates/ghostty-apprt-gtk/src/adw_version.rs

@@ -2,8 +2,10 @@
 
 use crate::gtk_version::Version;
 
-/// The libadwaita feature level this crate is compiled against (`v1_5`).
-pub const COMPTIME_VERSION: Version = (1, 5, 0);
+/// The libadwaita version this crate is compiled against (pkg-config
+/// `libadwaita-1`, see `build.rs`).
+pub const COMPTIME_VERSION: Version =
+    crate::gtk_version::parse_version(env!("GHOSTTY_ADW_VERSION"));
 
 /// Returns the runtime libadwaita version.
 #[allow(unsafe_code)]