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/error.rs

@@ -0,0 +1,48 @@
+//! The error type returned by CLI actions.
+
+use ghostty_config::cli_args::ArgError;
+
+/// The name used by [`ArgError::Other`] to signal that `--help`/`-h` was
+/// passed (Zig: `Action.help_error`).
+pub const HELP_ERROR_NAME: &str = "ActionHelpRequested";
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    /// This should be returned by actions that want to print the help text
+    /// (Zig: `error.ActionHelpRequested`).
+    #[error("ActionHelpRequested")]
+    ActionHelpRequested,
+
+    /// Argument parsing failed.
+    #[error("{0}")]
+    Args(ArgError),
+
+    /// Loading the configuration failed.
+    #[error("{0}")]
+    Config(#[from] ghostty_config::config::Error),
+
+    #[error("{0}")]
+    Io(#[from] std::io::Error),
+
+    /// The action exists but depends on functionality that is not ported yet.
+    #[error("the `+{0}` action is not yet available in this build")]
+    NotYetAvailable(&'static str),
+
+    #[error("{0}")]
+    Other(String),
+}
+
+impl From<ArgError> for Error {
+    fn from(e: ArgError) -> Self {
+        match e {
+            ArgError::Other(ref n) if n == HELP_ERROR_NAME => Error::ActionHelpRequested,
+            e => Error::Args(e),
+        }
+    }
+}
+
+impl From<std::fmt::Error> for Error {
+    fn from(_: std::fmt::Error) -> Self {
+        Error::Other("FormatError".to_string())
+    }
+}