Add Rust revival engine for Super Skidmarks

Cross-platform (Windows/macOS/Linux) engine that plays the original
Amiga data straight from the ADF images:

- ADF (OFS/FFS), LHA and CrunchMania (CrM!/CrM2) readers
- Track decoding: 24 tracks of 1024x512 16-colour planar art, height
  maps and lap gates on an isometric ground plane
- Vehicle decoding: 8 cars, 32 headings x 25 tilt frames of 64x32
  AGA sprites
- Reconstructed handling, AI, race rules, menus and synthesised sound
  (disk 1 with the executable, palettes and audio is not in the set)
- info/extract/bench/trace/render tools, format notes, CI builds

README.md

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+# Skids: a Super Skidmarks revival
+
+A cross-platform (Windows, macOS, Linux) engine written in Rust that plays
+*Super Skidmarks* (Acid Software, 1995) on the original Amiga data.
+
+It reads the game's ADF disk images directly: it unpacks the LHA archives
+on them, decrunches the CrunchMania-packed files, and decodes the planar
+track graphics and AGA sprite banks. No game assets are compiled into the
+program; you supply the disks.
+
+## What works
+
+- All 24 tracks across the four track files. Each has its isometric height
+  map and lap gates.
+- All 8 vehicles (Mini, Beetle, Porsche, Formula 1, Midget, Truck, Police,
+  Cow), with 32 headings and 25 body-tilt frames for hills.
+- 1 or 2 players (split screen) plus up to 7 computer drivers.
+- Power-slide handling, slopes, car-to-car bumping, and skid marks burnt
+  into the track.
+- Lap and position tracking, lap times, and a results table.
+- Procedural engine, tyre and crash sound.
+
+## What's reconstructed
+
+Disk 1 of the six-disk set is missing from this archive. It held the
+executable, palettes, sound and music. As a result:
+
+- **Handling, AI and race rules** are new code written to feel like the
+  original, not a translation of the original 68000 code.
+- **Colours** come from a reconstructed palette, built around how the
+  tracks use their 16 colour indices. If you have the real palettes, put
+  them in a `palettes/` folder next to the disks as `.pal` files (16 lines
+  of `RRGGBB`):
+  - `track1-3.pal` for one track
+  - `track1.pal` for all six tracks in a file
+  - `default.pal` for everything
+- **Sound** is synthesised.
+
+If you find disk 1, drop it in with the others. Anything it contains under
+`track/` or `vehicles/` is picked up automatically. The format notes in
+[docs/FORMATS.md](docs/FORMATS.md) cover everything reverse engineered so
+far.
+
+## Running
+
+```sh
+cargo run --release -- --data /path/to/adfs
+```
+
+Without `--data`, the game looks in the current directory and then next to
+the executable, so running it from this repository's root just works.
+
+| Action      | Player 1                              | Player 2 |
+|-------------|---------------------------------------|----------|
+| Accelerate  | ↑ (or W in one-player games)          | W        |
+| Brake / reverse | ↓ (or S)                          | S        |
+| Steer       | ← → (or A D)                          | A D      |
+| Pause       | P                                     |          |
+| Leave race  | Esc                                   |          |
+
+Options: `--scale 1|2|4` (window size), `--mute`.
+
+### Tools
+
+```sh
+skids info    --data DIR                  # list tracks and vehicles found
+skids extract --data DIR --out pngs/      # dump every track (with gates) and car sheet
+skids bench   --data DIR --seconds 120    # race CPU cars on every track: laps and time on road
+skids trace   --data DIR --track 11 --out t.png   # plot CPU racing lines
+skids render  --data DIR --track 3 --out shot.png # headless screenshot
+```
+
+## Building
+
+You need a stable Rust toolchain.
+
+- **Linux:** install the ALSA and X11 development packages, e.g.
+  `sudo apt install libasound2-dev libx11-dev libxkbcommon-dev`. To build
+  without sound (no ALSA needed), use `cargo build --release --no-default-features`.
+- **macOS / Windows:** `cargo build --release` works as is.
+
+GitHub Actions builds all three platforms on every push
+(`.github/workflows/build.yml`).
+
+## Layout
+
+```
+src/formats/   ADF (OFS/FFS), LHA and CrunchMania readers
+src/data/      track, vehicle and palette decoding; locating the game files
+src/game/      physics, AI and race rules
+src/render/    software renderer at 320×256 (PAL low-res) and a bitmap font
+src/audio.rs   synthesised sound (cpal)
+src/app.rs     menus, race screens and results
+```
+
+## Credits
+
+*Super Skidmarks* is by Acid Software. This project is an unofficial
+revival for preservation. The CrunchMania bitstream layout follows Teemu
+Suutari's [ancient](https://github.com/temisu/ancient) (BSD-2-Clause).