feat(offaxis): clean-room Kooima off-axis projection in Rust/WASM (ADR-324)

New leaf crate v2/crates/ruview-offaxis implementing ADR-324's projection
core from the published math only (Kooima 2008 generalized perspective
projection; Casiez 2012 one-euro filter) — no code from the unlicensed
prior-art repo. Dependency-free native core; wasm-bindgen surface gated to
wasm32 (cdylib+rlib, ~54 KB wasm after bindgen).

- projection: Screen (3 corners, any orientation) + off_axis() -> typed
  errors, never NaN matrices; column-major f64 (three.js Matrix4 layout).
  Tests pin the defining invariants: screen corners -> NDC corners for a
  grid of eye positions and tilted screens; screen-plane points are
  eye-invariant; centered eye reduces to the symmetric frustum; near/far
  map to NDC -1/+1.
- filter: one-euro with injected timestamps (no clock in crate);
  monotonicity/convergence/NaN-rejection tests.
- rf: field-peak extraction mirroring field_localize.rs constants
  (X_SCALE 0.6, Z_SCALE 0.5, PEAK_THRESHOLD 0.35) and the Tier B
  coarse-parallax stage (deadband, gain, hard clamp) so over-claiming is
  impossible at the API level. No accuracy numbers asserted.
- wasm: OffAxisCamera + RfParallax bindgen classes; per-frame updates hold
  last good state instead of throwing.
- benches (criterion): full Tier B frame ~598 ns; argmax scan optimized
  -18%/-33% (20x20/100x100). MEASURED table + reproducer in README.
- examples/three.js/demos/07-off-axis-window.html: demo with SYNTHETIC
  mouse simulator and labeled RF Tier B mode ('coarse body parallax - not
  head tracking'), physical calibration panel, /ws/sensing input, and a
  build-instructions overlay when the local pkg/ output is missing
  (generated artifacts stay uncommitted; .gitignore entry added).
- Validated 23 unit tests + doctest, clippy clean, wasm32 release build,
  Node smoke test of the bindgen output, and a headless-Chromium run of
  the demo (engine load, eye response, mode labels, ws failure path).
- ADR-324: header + section 2.5 amendment recording the Rust/WASM core.

Co-Authored-By: claude-flow <ruv@ruv.net>
Claude-Session: https://claude.ai/code/session_01BU3NcEgTpAVvu5QGtw4czT

docs/adr/ADR-324-off-axis-head-coupled-perspective-demo.md

@@ -2,7 +2,7 @@
 
 | Field | Value |
 |-------|-------|
-| **Status** | Proposed |
+| **Status** | Proposed (core implemented — see §2.5) |
 | **Date** | 2026-08-16 |
 | **Deciders** | ruv |
 | **Codename** | **off-axis-mode** |
@@ -195,6 +195,21 @@ in this ADR solely so nobody ships it informally without those gates.
    embeddings are sent to the server. RF data continues to obey ADR-307's
    privacy invariants (pseudonymous, coarse, rotatable).
 
+### 2.5 Implementation status (2026-08-16 amendment)
+
+The projection core shipped as a **Rust crate compiled to WASM** rather than
+the inline JS module §2.3 anticipated — a strict upgrade with the same
+surface: `v2/crates/ruview-offaxis` (dependency-free native core; wasm-bindgen
+only on wasm32) implements the Kooima projection, the one-euro filter, the
+field-peak mapping (constants mirroring `field_localize.rs`), and the Tier B
+coarse-parallax stage with its deadband/gain/clamp bounds enforced in Rust.
+`examples/three.js/demos/07-off-axis-window.html` consumes the wasm-bindgen
+output (built locally per the crate README; generated artifacts are not
+committed). Validation and `MEASURED` benchmarks live in the crate README.
+The demo ships with a `SYNTHETIC`-labeled mouse simulator and the labeled
+Tier B RF mode; a Tier A fine tracker connects through
+`OffAxisCamera.update_normalized` and remains host-provided.
+
 ## 3. Options considered
 
 | Option | Verdict | Why |