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/ghostty.rs

@@ -148,23 +148,9 @@ impl Action {
     /// function, i.e. `help_strings.Action.<name>`), without trailing newline.
     #[must_use]
     pub fn help_text(self) -> &'static str {
-        match self {
-            Action::Version => include_str!("help/version.txt"),
-            Action::Help => include_str!("help/help.txt"),
-            Action::ListFonts => include_str!("help/list-fonts.txt"),
-            Action::ListKeybinds => include_str!("help/list-keybinds.txt"),
-            Action::ListThemes => include_str!("help/list-themes.txt"),
-            Action::ListColors => include_str!("help/list-colors.txt"),
-            Action::ListActions => include_str!("help/list-actions.txt"),
-            Action::SshCache => include_str!("help/ssh-cache.txt"),
-            Action::EditConfig => include_str!("help/edit-config.txt"),
-            Action::ShowConfig => include_str!("help/show-config.txt"),
-            Action::ValidateConfig => include_str!("help/validate-config.txt"),
-            Action::ShowFace => include_str!("help/show-face.txt"),
-            Action::CrashReport => include_str!("help/crash-report.txt"),
-            Action::Boo => include_str!("help/boo.txt"),
-            Action::NewWindow => include_str!("help/new-window.txt"),
-        }
+        // Generated by `build.rs` (via `ghostty-helpgen`) from the doc
+        // comment of each action's `run` function.
+        include!(concat!(env!("OUT_DIR"), "/action_help.rs"))
     }
 
     /// Run the action. `args` is the full argument vector (including