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-build-data/src/chunks_zsh.rs

@@ -0,0 +1,58 @@
+// Generated from the Zig multiline strings of extra/zsh.zig. Do not edit.
+pub const C0: &str = r####"#compdef ghostty
+
+_fonts () {
+  local font_list=$(ghostty +list-fonts | grep -Z '^[A-Z]')
+  local fonts=(${(f)font_list})
+  _describe -t fonts 'fonts' fonts
+}
+
+_themes() {
+  local theme_list=$(ghostty +list-themes | sed -E 's/^(.*) \(.*$/\1/')
+  local themes=(${(f)theme_list})
+  _describe -t themes 'themes' themes
+}
+"####;
+pub const C1: &str = r####"_ghostty() {
+  typeset -A opt_args
+  local context state line
+  local opt=('-e' '--help' '--version')
+
+  _arguments -C \
+    '1:actions:->actions' \
+    '*:: :->rest' \
+
+  if [[ "$line[1]" == "--help" || "$line[1]" == "--version" || "$line[1]" == "-e" ]]; then
+    return
+  fi
+
+  if [[ "$line[1]" == -* ]]; then
+    _config
+    return
+  fi
+
+  case "$state" in
+    (actions)
+      local actions; actions=(
+"####;
+pub const C2: &str = r####"      )
+      _describe '' opt
+      _describe -t action 'action' actions
+    ;;
+    (rest)
+      if [[ "$line[2]" == "--help" ]]; then
+        return
+      fi
+
+      local help=('--help')
+      _describe '' help
+
+      case $line[1] in
+"####;
+pub const C3: &str = r####"      esac
+    ;;
+  esac
+}
+
+_ghostty "$@"
+"####;