ans: order-0 rANS coder + WGSL asset compression

Adds src/util/ans.{h,cc}, a per-chunk-adaptive order-0 rANS entropy
coder. Decoder is always built; encoder is gated on ANS_ENABLE_ENCODER
(tools only). Both sides take an optional 256-entry initial_counts
table to seed the adaptive model.

The per-chunk initial state is (1 << kBits). Higher initial states
(e.g. with a signature packed into the upper bits) force a renorm-emit
at iter 0 that the decoder never consumes, corrupting multi-chunk
streams once stats become skewed.

Asset pipeline:
- AssetRecord gains 'compression' and 'uncompressed_size' fields.
- asset_packer scans every WGSL file to build a corpus-wide byte
  histogram, then ANS-encodes each shader using that histogram as the
  seed. Histogram and accessor are emitted alongside the asset table.
  Round-trip verification runs at pack time for every compressed
  asset; failures fall back to uncompressed storage.
- asset_manager decompresses on first GetAsset(), caches the
  heap-allocated buffer, and DropAsset / ReloadAssetsFromFile free it
  along with the procedural cache.
- Disk-load (dev) builds are unchanged: WGSL paths stay as filenames.

Tests:
- src/tests/util/test_ans.cc: roundtrip variants (empty, single byte,
  single-symbol run, all-zeros, random uniform/skewed, repeated ASCII),
  seeded-vs-uniform compression, rejection of mismatched counts /
  corruption / truncation, PeekUncompressedSize.
- 37/37 dev, 36/36 STRIP_ALL.

Compression observed: WGSL shaders shrink to ~0.62-0.71x in the main
workspace (81 of 105 assets qualify).

Docs:
- doc/ANS.md (new): algorithm, bitstream, API, asset pipeline
  integration, compression numbers, limitations, tests.
- doc/ASSET_SYSTEM.md: new Compression section + updated technical
  guarantees for compressed assets.
- doc/COMPLETED.md: May 2026 entry.
- PROJECT_CONTEXT.md: Build status line mentions WGSL ANS compression.
- CLAUDE.md, GEMINI.md: tier-3 build doc list includes ANS.md.

1 files changed, 1 insertions, 1 deletions

diff --git a/PROJECT_CONTEXT.md b/PROJECT_CONTEXT.md
index d7fc771..43ce2f1 100644
--- a/PROJECT_CONTEXT.md
+++ b/PROJECT_CONTEXT.md
@@ -38,7 +38,7 @@
 - **3D:** Hybrid SDF/rasterization with BVH. Binary scene loader. Blender pipeline.
 - **Effects:** CNN post-processing: CNNEffect (v1) and CNNv2Effect operational. CNN v2: sigmoid activation, storage buffer weights (~3.2 KB), 7D static features, dynamic layers. Training stable, convergence validated. **CNN v3 Phases 1–9 complete** + runtime pipeline operational: `GBufferEffect` (MRT raster + sphere impostors + SDF shadow pass) → `GBufDeferredEffect` (albedo×diffuse) in `cnn_v3_test`; debug sequence adds `CNNv3Effect` → `GBufViewEffect`. Training bugs fixed: dec0 ReLU removed, FiLM MLP loaded from `.bin`. Parity validated: max_err=4.88e-4. See `cnn_v3/docs/HOWTO.md`.
 - **Tools:** CNN test tool operational. Texture readback utility functional. Timeline editor (web-based, beat-aligned, audio playback).
-- **Build:** Asset dependency tracking. Size measurement. Hot-reload (debug-only). WSL (Windows 10) supported: native Linux build and cross-compile to `.exe` via `mingw-w64`.
+- **Build:** Asset dependency tracking. Size measurement. Hot-reload (debug-only). WSL (Windows 10) supported: native Linux build and cross-compile to `.exe` via `mingw-w64`. WGSL shaders ANS-compressed in embedded (STRIP_ALL) builds with a corpus-derived ASCII histogram, ~0.62–0.71× on the main workspace (see `doc/ANS.md`).
 - **Sequence:** DAG-based effect routing with explicit node system. Python compiler with topological sort and ping-pong optimization. 18 effects operational (Passthrough, Placeholder, GaussianBlur, Heptagon, Particles, RotatingCube, Hybrid3D, Flash, PeakMeter, Scene1, Scene2, Scratch, Ntsc, NtscYiq, GBufferEffect, CNNv3Effect, GBufDeferredEffect, GBufViewEffect). Effect times are absolute (seq_compiler adds sequence start offset). See `doc/SEQUENCE.md`.
 - **Testing:** **38/38 passing**.