feat(config): port the configuration system and CLI argument parser

Ports ZIG/src/config (minus C/WASM APIs) and cli/{args,CommaSplitter,
diagnostics}.zig into ghostty-config:
- all 202 options with exact names, types, defaults and verbatim docs,
  declared through one config_struct! macro; Zig's comptime reflection is
  replaced by the ConfigField/CliTarget traits
- loading: default XDG files, -e, config-file includes (optional '?',
  cycle detection), themes incl. light:/dark: pairs, conditional config,
  replay, finalize() derived defaults, clone/changed diffing for reload
- Linux/GTK default keybinds built on ghostty_input::binding::Set
- formatter producing +show-config output

Verified against the installed Ghostty 1.3.1: `+show-config --default`
and `--default --docs` match byte for byte (except gtk-opengl-debug,
which differs between debug/release builds), as do two complex loaded
configs.

Open items (docs/rewrite/notes/ghostty-config.md): url regex needs an
Oniguruma-compatible engine (onig) in the renderer; some font/terminal
types are local copies awaiting integration; KeyRemapSet equality is
order sensitive unlike Zig.

Test Plan:
- cargo test -p ghostty-config (255 tests)
- compare `ghostty +show-config --default --docs` with our formatter

crates/ghostty-config/src/clipboard_codepoint_map.rs

@@ -0,0 +1,63 @@
+//! ClipboardCodepointMap is a map of codepoints to replacement values
+//! for clipboard operations. When copying text to clipboard, matching
+//! codepoints will be replaced with their mapped values.
+
+/// Replacement value for a codepoint range.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Replacement {
+    /// A single replacement codepoint.
+    Codepoint(u32),
+    /// A UTF-8 encoded string to replace with.
+    String(String),
+}
+
+/// One entry of the map.
+///
+/// TODO(integration): this mirrors `terminal/formatter.zig` `CodepointMap`;
+/// replace with `ghostty_terminal::formatter::CodepointMap` once available.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Entry {
+    /// Unicode codepoint range to replace.
+    /// Asserts: range[0] <= range[1]
+    pub range: [u32; 2],
+    /// Replacement value for this range.
+    pub replacement: Replacement,
+}
+
+/// The list of entries.
+///
+/// Note: we do a linear search because we expect to always have very
+/// few entries, so the overhead of a binary search is not worth it.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct ClipboardCodepointMap {
+    pub list: Vec<Entry>,
+}
+
+impl ClipboardCodepointMap {
+    /// Add an entry to the map.
+    ///
+    /// For conflicting codepoints, entries added later take priority over
+    /// entries added earlier.
+    pub fn add(&mut self, entry: Entry) {
+        assert!(entry.range[0] <= entry.range[1]);
+        self.list.push(entry);
+    }
+}
+
+#[cfg(test)]
+#[allow(clippy::unwrap_used)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn add_and_clone() {
+        let mut m = ClipboardCodepointMap::default();
+        m.add(Entry {
+            range: [1, 2],
+            replacement: Replacement::String("x".into()),
+        });
+        let c = m.clone();
+        assert_eq!(m, c);
+        assert_eq!(c.list.len(), 1);
+    }
+}