feat(cli): port ghostty +action CLI commands

Ports ZIG/src/cli into ghostty-cli: action detection/dispatch with
per-action --help, and the actions help, version, list-actions,
list-colors, list-keybinds, list-themes (plain listing plus an
interactive ratatui browser mirroring Ghostty's libvaxis UI),
show-config, validate-config, edit-config, crash-report (listing),
ssh-cache and boo (235 embedded frames).

Verified byte-for-byte against the installed Ghostty 1.3.1 for stdout,
stderr and exit codes of most actions, incl. tty output in a pty at
widths 20-200. Known differences: +list-colors --plain prints all 782
colors (Ghostty truncates at 617 because it never flushes), +version
has placeholder build info until build_info::set is wired up.

Deferred: list-fonts, show-face (need font discovery integration) and
new-window (needs GTK IPC); they return NotYetAvailable for now.

Test Plan:
- cargo test -p ghostty-cli (86 tests)
- cargo run -p ghostty-cli --example cli -- +list-keybinds --plain
  and diff against `ghostty +list-keybinds --plain`

crates/ghostty-cli/src/show_config.rs

@@ -0,0 +1,128 @@
+//! `+show-config` (ZIG/src/cli/show_config.zig).
+
+use std::io::Write;
+
+use ghostty_config::config::Config;
+use ghostty_config::config_struct;
+use ghostty_config::file_formatter::FileFormatter;
+
+use crate::error::Error;
+
+config_struct! {
+    pub struct Options {
+        /// If true, do not load the user configuration, only load the defaults.
+        "default" => default: bool = false,
+
+        /// Only show the options that have been changed from the default.
+        /// This has no effect if `--default` is specified.
+        "changes-only" => changes_only: bool = true,
+
+        /// If true print the documentation above each option as a comment,
+        /// if available.
+        "docs" => docs: bool = false,
+    }
+}
+cli_options!(Options, help);
+
+/// The `show-config` command shows the current configuration in a valid Ghostty
+/// configuration file format.
+///
+/// When executed without any arguments this will output the current
+/// configuration that is different from the default configuration. If you're
+/// using the default configuration this will output nothing.
+///
+/// If you are a new user and want to see all available options with
+/// documentation, run `ghostty +show-config --default --docs`.
+///
+/// The output is not in any specific order, but the order should be consistent
+/// between runs. The output is not guaranteed to be exactly match the input
+/// configuration files, but it will result in the same behavior. Comments,
+/// whitespace, and other formatting is not preserved from user configuration
+/// files.
+///
+/// Flags:
+///
+///   * `--default`: Show the default configuration instead of loading
+///     the user configuration.
+///
+///   * `--changes-only`: Only show the options that have been changed
+///     from the default. This has no effect if `--default` is specified.
+///
+///   * `--docs`: Print the documentation above each option as a comment,
+///     This is very noisy but is very useful to learn about available
+///     options, especially paired with `--default`.
+pub fn run(args: &[String]) -> Result<u8, Error> {
+    let mut opts = Options::default();
+    crate::parse_options(&mut opts, args)?;
+
+    let config = if opts.default {
+        Config::new_default()
+    } else {
+        Config::load()?
+    };
+
+    let text = format_config(&config, &opts)?;
+    let mut stdout = std::io::stdout().lock();
+    stdout.write_all(text.as_bytes())?;
+    stdout.flush()?;
+    Ok(0)
+}
+
+/// Format `config` according to `opts`.
+pub fn format_config(config: &Config, opts: &Options) -> Result<String, Error> {
+    let fmt = FileFormatter {
+        config,
+        changed: !opts.default && opts.changes_only,
+        docs: opts.docs,
+    };
+    let mut out = String::new();
+    fmt.format(&mut out)?;
+    Ok(out)
+}
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::unwrap_used)]
+    use super::*;
+
+    #[test]
+    fn default_changes_only_is_empty() {
+        let config = Config::new_default();
+        let opts = Options::default();
+        assert_eq!("", format_config(&config, &opts).unwrap());
+    }
+
+    #[test]
+    fn default_docs_has_comments() {
+        let config = Config::new_default();
+        let opts = Options {
+            default: true,
+            docs: true,
+            ..Options::default()
+        };
+        let s = format_config(&config, &opts).unwrap();
+        assert!(s.contains("# The font families to use."));
+        assert!(s.contains("\nfont-size = 12\n"));
+    }
+
+    #[test]
+    fn options_parse() {
+        let mut opts = Options::default();
+        let args: Vec<String> = [
+            "ghostty",
+            "+show-config",
+            "--default",
+            "--changes-only=false",
+        ]
+        .iter()
+        .map(ToString::to_string)
+        .collect();
+        crate::parse_options(&mut opts, &args).unwrap();
+        assert!(opts.default);
+        assert!(!opts.changes_only);
+        assert!(matches!(
+            crate::parse_options(&mut opts, &["g".into(), "--help".into()]),
+            Err(Error::ActionHelpRequested)
+        ));
+    }
+}