Initialise native Rust port of Ratchet & Clank: Going Commando

Sets up the foundation for reimplementing the PS2 game in Rust rather than
emulating it. Nothing is implemented yet; this is the scaffold, the verified
target and the working agreements that keep a long project coherent.

Target disc, verified against a real image:

  SCUS_972.68 v1.01, USA Black Label, NTSC 60 Hz
  boot ELF 2,618,684 bytes, SHA-1 bacda860...d098a77, entry 0x00131AE8

The entry point independently matches the value recorded by the rac2-gc-decomp
community reference, which cross-confirms the identification. This is the exact
build the upstream research pins; Greatest Hits v2.00 is a different binary and
is not the target. NTSC matters beyond label compatibility: PAL discs run 50 Hz,
which would make chargeboots and other speed-sensitive movement run at 5/6
speed. Verifying the disc before writing movement code avoids discovering that
in Phase 5.

Contents:

- Five-crate workspace (formats, extract, game, video, engine) on Bevy 0.19.1,
  matching the version ReRAC uses so its Graphics Synthesizer and VU work stays
  portable. `cargo check --workspace` is clean.

- tools/identify-disc.py, which reproduces the identification against any
  disc image and distinguishes a truncated dump from a non-PS2 image.

- .githooks/pre-commit, refusing game data from entering git history: disc
  image extensions, asset directories, container signatures at offset 0, and
  files over 50 MiB. Verified against seven cases including a disc image
  renamed to look like source. Now that this pushes to a remote, this matters
  more than it would have locally.

- AGENTS.md, the operating agreements: no game data ever, reproduce the PS2
  float model rather than approximating it, bound every read, verify against
  the real disc.

- PROVENANCE.md, recording that this follows ReRAC (ISC) and learns from
  rac2-gc-decomp (MIT). Wrench is used as a written specification only and no
  GPLv3 code is copied, since that would relicense everything derived from it.
  RAC2Decomp is explicitly not used: its provenance is disputed in the upstream
  community reference, and it targets the wrong region.

- docs/roadmap.md, phased so the riskiest unknowns are retired early. The two
  that matter: overlay relocation transfers from ReRAC and makes 27 level
  overlays tractable, while VU1 microcode is binary and is the hardest single
  item. Phase 5 is a deliberately scoped Veldin vertical slice as the go/no-go.

crates/gc-game/src/lib.rs

@@ -0,0 +1,38 @@
+//! Game logic for *Ratchet & Clank: Going Commando* (PS2).
+//!
+//! The rules, systems and behaviour of the game, reimplemented from the
+//! original code rather than wrapped around it. No emulation, no interpreter:
+//! this is a Rust implementation that is meant to behave the way the game does.
+//!
+//! # What belongs here
+//!
+//! * `hero`       - Ratchet's controller. Movement on a **spherical** planet,
+//!                  which is what distinguishes this game: reaching for the
+//!                  camera and the collision code changes gravity handling
+//!                  across the whole world, and is the main reason the first
+//!                  game's movement code does not transfer.
+//! * `chargeboots`- hold and release timing, chained jumps and the dash.
+//! * `weapons`    - the wrench and the weapon set, plus the weapon modification
+//!                  system (per-weapon bitmasks: lock-on, shock, acid, ...).
+//! * `gadgets`    - the Pyrocitor, Bomb Glove, Glove of Doom and friends.
+//! * `moby_update`- the per-class update dispatch, driven by each level's
+//!                  `lvl.vtbl` class table. Classes that are identical across
+//!                  levels are shared; the rest are resolved through the
+//!                  overlay relocator in `gc-formats`.
+//! * `collision`  - queries against the collision world.
+//! * `progression`- bolts, the Gadgetron vendor, RPG upgrades and unlocks.
+//! * `save_game`  - the IFF chunk save format, and importing a Ratchet & Clank
+//!                  (2002) save to unlock the legacy weapons for free.
+//! * `memcard`    - the 25-state memory-card finite state machine and its UI.
+//!
+//! # The float model
+//!
+//! The Emotion Engine's FPU is not IEEE-754 in every respect: it has no
+//! denormals, and rounding differs in places. Gameplay code here reproduces
+//! that model rather than using Rust's native `f32`, because the difference is
+//! visible in the movement and the camera. See `docs/plan/float-model.md`.
+//!
+//! # Timing
+//!
+//! The game is 60 Hz (this disc is NTSC). Constants are expressed per tick at
+//! that rate. PAL discs run 50 Hz and would need different timing throughout.