v0.2.0 — visual remaster + native Metal backend

v0.2.0 adds an opt-in visual remaster and a native Metal graphics backend on
macOS, layered on top of the v0.1.0 faithful port. Everything is behind flags:
the byte-faithful 1997 look is preserved (--faithful), and no visual option
changes the gameplay simulation. Still a community-iteration release — bring your
own legally-owned ROM.

Highlights

• 🎬 One-switch visual modes. --faithful (byte-faithful original),
  --faithful-hd (the faithful look at 2× supersampling, HD-pack-ready), and
  --remaster (the full cinematic stack). See
  docs/VISUAL_MODES.md.
• ✨ Remaster post-processing — screen-space ambient occlusion, bloom, filmic
  tonemap, per-level colour grade, FXAA, contrast-adaptive sharpen, vignette,
  output dither, and 2× supersampling. Each effect is an independent
  Video.*/GE007_* toggle.
• 🖥️ Native Metal graphics backend on macOS (GE007_RENDERER=metal, selected
  automatically by --remaster), at parity with the GL reference path and without
  the Apple GL-over-Metal ambient-occlusion hang.
• 🧵 Smoother frame pacing — a sub-millisecond deadline pacer that locks the
  frame interval to the display, fixing periodic judder while turning/strafing.
• 🖼️ HD texture pipeline — build HD packs from your own ROM dump with
  tools/texpack (Real-ESRGAN / procedural synthesis). Packs are ROM-derived and
  are never distributed.
• 🔦 Opt-in lighting features (default-off, under review) — smoothed
  environment normals that remove baked per-quad lighting seams
  (GE007_ENV_SMOOTH_NORMALS=1) and destructible light fixtures
  (GE007_SHOOT_OUT_LIGHTS=1).
• 🕹️ Modern feel options (on by default; all reverted by --faithful) — a
  modern crosshair, hit markers, a tactical minimap, and widescreen FOV; plus
  opt-in aim-down-sights (Input.AdsEnabled=1) and 2–4 player split-screen
  (--multiplayer --players N).

Rails

Every remaster feature is behind a named flag, defaults to a byte-identical
faithful baseline, and never reads or writes the gameplay simulation. All
HD/ROM-derived assets are local-only and never committed.