refactor(config): parse config values from raw bytes like Zig

Zig parses config values (cli/args.zig, Config.zig field parsers,
config/string.zig) from raw byte slices, and each field type decides
whether it requires UTF-8 (InvalidValue otherwise) or stores bytes. The
port escape-encoded raw bytes into Strings at the line reader and let
fields parse the escaped text, so fields could observe encoding
artifacts; successive audits kept finding such leaks (RV5-RV8).

Field parsers now receive the original bytes: text fields validate UTF-8
where Zig does, byte/path fields store bytes (EncodedOs/OsString). This
resolves all 9 RV8 findings (docs/rewrite/notes/review-rv8-codex.md),
each with a regression test: Windows path conversion fails with
BadPathName instead of substituting U+FFFD; Windows process launch uses
strict UTF-8 like Zig's Command; the WTF-8 decoder accepts paired-
surrogate encodings like Zig; literal U+FDD0 Unicode key triggers;
selection-word-chars and clipboard-codepoint-map reject invalid UTF-8;
font style / codepoint-map family names use original bytes; C title
actions forward bytes; D-Bus new-window/Flatpak conversions match Zig.
Design, sweep and validation: docs/rewrite/notes/final-bytes-refactor.md.

Also moves the bundled iTerm2-Color-Schemes license out of
resources/themes/ so +list-themes no longer lists it as a theme
(output is now byte-identical to Ghostty 1.3.1).

Done by Codex (gpt-6-astra), reviewed and verified by the orchestrator.

Test Plan:
- cargo test --workspace --no-fail-fast (3428 passed, exit 0)
- just check-macos (both), just check-windows, just check-wasm
- +show-config --default --docs, +list-keybinds, +list-actions --docs,
  +list-themes --plain compared with /usr/bin/ghostty

crates/ghostty-apprt-gtk/src/css.rs

@@ -113,6 +113,13 @@ impl CssProviders {
                 Path::Optional(path) => (path.to_path(), true),
                 Path::Required(path) => (path.to_path(), false),
             };
+            let path = match path {
+                Ok(path) => path,
+                Err(error) => {
+                    log::warn!("invalid custom CSS path: {error}");
+                    continue;
+                }
+            };
             let shown = path.display();
             let meta = match std::fs::metadata(&path) {
                 Ok(m) => m,
@@ -215,7 +222,7 @@ pub fn runtime_css(config: &Config, gtk_416: bool) -> String {
     }
 
     if let Some(family) = &config.window_title_font_family {
-        let family = ghostty_os::osbytes::config_str_to_text(family);
+        let family = family.to_text_lossy();
         let _ = write!(
             out,
             ".window headerbar {{\n  font-family: \"{family}\";\n}}\n"