feat: port GTK version fallbacks, helpgen, bench modes, CLI leftovers

- apprt-gtk: Ghostty's runtime+build-time version gating (at_least)
  with cargo features adw_1_3/adw_1_4/adw_1_5/gtk_4_16 (default on) and
  the fallbacks for older libraries: MessageDialog (adw < 1.5),
  clipboard dialog without SwitchRow, pre-Banner debug warning and
  child-exited widgets, the old about dialog, GTK 4.16 CSS error source
  bytes. The minimum stays GTK 4.14 / libadwaita 1.5 (Ghostty's floor).
  The root build links with -z lazy so version-gated symbols don't keep
  older libraries from loading.
- ghostty-helpgen (port of helpgen.zig) generates CLI action help and
  keybinding action docs from doc comments at build time, replacing the
  checked-in help/*.txt; +help and +list-actions --docs stay
  byte-identical to Ghostty 1.3.1.
- ghostty-bench: libc wcwidth mode and separate simd/table and
  uucode/table code paths like Zig.
- ghostty-cli: Windows branches of edit-config, list-colors,
  list-keybinds and boo; ssh-cache DiskCache flock locking (no-op on
  Windows, as in Zig) with an exclusivity test.

Test Plan:
- cargo test --workspace
- diff <(cargo run -q -- +list-actions --docs) \
  <(ghostty +list-actions --docs)

crates/ghostty-cli/src/tui.rs

@@ -264,9 +264,20 @@ fn write_style_change(w: &mut dyn Write, cursor: &Style, next: &Style) -> std::i
     Ok(())
 }
 
+/// Fixed `(cols, rows)` used on Windows instead of querying the tty.
+#[cfg(windows)]
+const WINDOWS_WINSIZE: (u16, u16) = (120, 24);
+
 /// The terminal size in columns and rows (`vaxis.Tty.getWinsize`).
 #[must_use]
 pub fn window_size() -> (u16, u16) {
+    // On Windows we use some default; it doesn't really matter for what we're
+    // doing because we don't do any wrapping (rows = 24, cols = 120).
+    #[cfg(windows)]
+    {
+        WINDOWS_WINSIZE
+    }
+    #[cfg(not(windows))]
     ratatui::crossterm::terminal::size().unwrap_or((80, 24))
 }