fix: inspector font/formatting, FreeType-only backend on Apple

Resolves the parity items of docs/rewrite/notes/review-rv17-codex.md
(final-Z20.md):
- FreeType-only font backend is also available on Apple targets
  (discovery-free, embedded emoji fonts); ghostty_surface_quicklook_font
  returns null for every backend except plain CoreText like Zig.
- The +list-fonts test keys off the font crate's selected backend
  (HAS_DISCOVERY), correct under feature unification and on Apple.
- Inspector font: 32 px rasterized with FreeType (dear-imgui freetype)
  like Ghostty; a new `visual-parity.sh inspector` scenario shows 0.031%
  differing pixels (hover highlight) vs the original on Linux. Windows,
  Apple and wasm keep stb_truetype at 32 px (registered as a deliberate
  deviation).
- Inspector DCS/APC descriptions follow Zig 0.15.2's formatting
  (checked by running Zig), incl. the terminal.Parser.Action prefix.
- The ImGui demo window appears only in dev-profile builds, mirroring
  Zig's .Debug-only gate.

Test Plan:
- cargo test --workspace --no-fail-fast (3582 passed)
- just check-macos (both, also with --features font-backend-freetype)
- scripts/visual-parity.sh inspector

crates/ghostty-inspector/build.rs

@@ -0,0 +1,14 @@
+//! Emits `cfg(ghostty_debug_build)` for the Cargo `dev` profile (Zig
+//! `builtin.mode == .Debug`). `debug_assertions` is not equivalent: the
+//! repository's `release` profile enables it, like Zig's `ReleaseSafe`.
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-env-changed=PROFILE");
+    println!("cargo:rustc-check-cfg=cfg(ghostty_debug_build)");
+    let profile = std::env::var("PROFILE").unwrap_or_default();
+    println!("cargo:rustc-env=GHOSTTY_BUILD_PROFILE={profile}");
+    if profile == "debug" {
+        println!("cargo:rustc-cfg=ghostty_debug_build");
+    }
+}