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/validate_config.rs

@@ -0,0 +1,113 @@
+//! `+validate-config` (ZIG/src/cli/validate_config.zig).
+
+use std::io::Write;
+
+use ghostty_config::config::Config;
+use ghostty_config::config_struct;
+
+use crate::error::Error;
+
+config_struct! {
+    pub struct Options {
+        /// The path of the config file to validate. If this isn't specified,
+        /// then the default config file paths will be validated.
+        "config-file" => config_file: Option<String> = None,
+    }
+}
+cli_options!(Options, help);
+
+/// The `validate-config` command is used to validate a Ghostty config file.
+///
+/// When executed without any arguments, this will load the config from the default
+/// location.
+///
+/// Flags:
+///
+///   * `--config-file`: can be passed to validate a specific target config file in
+///     a non-default location
+pub fn run(args: &[String]) -> Result<u8, Error> {
+    let mut opts = Options::default();
+    crate::parse_options(&mut opts, args)?;
+
+    let mut stdout = std::io::BufWriter::new(std::io::stdout().lock());
+    let result = run_inner(&opts, &mut stdout);
+    stdout.flush()?;
+    result
+}
+
+fn run_inner(opts: &Options, stdout: &mut dyn Write) -> Result<u8, Error> {
+    let mut cfg = Config::new_default();
+
+    // If a config path is passed, validate it, otherwise validate default configs
+    if let Some(config_path) = &opts.config_file {
+        let abs_path = std::fs::canonicalize(config_path)?;
+        cfg.load_file(&abs_path.to_string_lossy())?;
+        cfg.load_recursive_files()?;
+    } else {
+        cfg = Config::load()?;
+    }
+
+    cfg.finalize()?;
+
+    if !cfg.diagnostics.items().is_empty() {
+        for diag in cfg.diagnostics.items() {
+            writeln!(stdout, "{diag}")?;
+        }
+        return Ok(1);
+    }
+
+    Ok(0)
+}
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::unwrap_used)]
+    use super::*;
+
+    fn write_tmp(name: &str, content: &str) -> String {
+        let dir =
+            std::env::temp_dir().join(format!("ghostty-cli-vc-{}-{name}", std::process::id()));
+        std::fs::create_dir_all(&dir).unwrap();
+        let p = dir.join("config");
+        std::fs::write(&p, content).unwrap();
+        p.to_string_lossy().into_owned()
+    }
+
+    #[test]
+    fn validate_good_file() {
+        let p = write_tmp("good", "font-size = 14\n");
+        let opts = Options {
+            config_file: Some(p),
+        };
+        let mut out = Vec::new();
+        assert_eq!(0, run_inner(&opts, &mut out).unwrap());
+        assert_eq!(0, out.len());
+    }
+
+    #[test]
+    fn validate_bad_file_prints_diagnostics() {
+        let p = write_tmp("bad", "not-a-key = 1\nfont-size = abc\n");
+        let opts = Options {
+            config_file: Some(p.clone()),
+        };
+        let mut out = Vec::new();
+        assert_eq!(1, run_inner(&opts, &mut out).unwrap());
+        let s = String::from_utf8(out).unwrap();
+        assert!(
+            s.contains(&format!("{p}:1:not-a-key: unknown field\n")),
+            "{s}"
+        );
+        assert!(
+            s.contains(&format!("{p}:2:font-size: invalid value \"abc\"\n")),
+            "{s}"
+        );
+    }
+
+    #[test]
+    fn validate_missing_file_is_error() {
+        let opts = Options {
+            config_file: Some("/nonexistent/ghostty/config".into()),
+        };
+        assert!(run_inner(&opts, &mut Vec::new()).is_err());
+    }
+}