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

scripts/macos-crosscheck.sh

@@ -3,6 +3,8 @@
 # Uses `zig cc` wrappers for the few C build scripts in the dependency
 # tree; real macOS builds need none of this. See docs/rewrite/notes/macos-M1.md.
 # Usage: scripts/macos-crosscheck.sh [check|clippy] [target]
+# MACOS_CHECK_FEATURES="ghostty-font/font-backend-freetype" adds cargo features
+# (for example the FreeType-only font backend on Apple).
 set -euo pipefail
 cd "$(dirname "$0")/.."
 MODE=${1:-clippy}
@@ -54,8 +56,12 @@ CRATES=(-p ghostty-vt -p ghostty-unicode -p ghostty-datastruct -p ghostty-os -p
   -p ghostty-config -p ghostty-terminal -p ghostty-font -p ghostty-renderer -p ghostty-termio
   -p ghostty-core -p ghostty-apprt -p ghostty-inspector -p ghostty-lib -p ghostty-crash
   -p ghostty-bench -p ghostty-vt-capi)
+FEATURES=()
+if [ -n "${MACOS_CHECK_FEATURES:-}" ]; then
+  FEATURES=(--features "$MACOS_CHECK_FEATURES")
+fi
 if [ "$MODE" = clippy ]; then
-  cargo clippy --target "$TARGET" "${CRATES[@]}" --lib --tests -- -D warnings
+  cargo clippy --target "$TARGET" "${CRATES[@]}" "${FEATURES[@]}" --lib --tests -- -D warnings
 else
-  cargo check --target "$TARGET" "${CRATES[@]}" --lib --tests
+  cargo check --target "$TARGET" "${CRATES[@]}" "${FEATURES[@]}" --lib --tests
 fi