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/build.rs

@@ -125,8 +125,45 @@ fn build_mode() -> &'static str {
     }
 }
 
+/// Generates the per-action help table (Zig: `helpgen.zig` `genActions`):
+/// the doc comment of each action's `run` function becomes
+/// `Action::help_text`.
+fn gen_action_help(manifest_dir: &Path) {
+    let ghostty_rs = manifest_dir.join("src/ghostty.rs");
+    println!("cargo:rerun-if-changed={}", ghostty_rs.display());
+    let src = std::fs::read_to_string(&ghostty_rs).expect("read ghostty.rs");
+    let mut table = Vec::new();
+    for (variant, _) in ghostty_helpgen::enum_variant_docs(&src, "Action") {
+        // `ListFonts` -> `list_fonts` (file name, as Zig `Action.file`).
+        let mut file = String::new();
+        for (i, c) in variant.chars().enumerate() {
+            if c.is_ascii_uppercase() && i > 0 {
+                file.push('_');
+            }
+            file.push(c.to_ascii_lowercase());
+        }
+        let path = manifest_dir.join(format!("src/{file}.rs"));
+        println!("cargo:rerun-if-changed={}", path.display());
+        let text = std::fs::read_to_string(&path).expect("read action source");
+        let help = ghostty_helpgen::run_fn_doc(&text).unwrap_or_else(|| {
+            panic!("doc comment must be present on run function of the {file} action!")
+        });
+        table.push((variant, help));
+    }
+    assert!(!table.is_empty(), "no actions found");
+    let out = PathBuf::from(std::env::var_os("OUT_DIR").expect("OUT_DIR"));
+    std::fs::write(
+        out.join("action_help.rs"),
+        ghostty_helpgen::cli_help_match(&table),
+    )
+    .expect("write action_help.rs");
+}
+
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
+    gen_action_help(&PathBuf::from(
+        std::env::var_os("CARGO_MANIFEST_DIR").unwrap_or_default(),
+    ));
     println!("cargo:rerun-if-env-changed=RUSTC");
     let rustc = std::env::var("RUSTC").unwrap_or_else(|_| "rustc".into());
     let version = Command::new(rustc)