feat(cnn_v3): Phase 1 complete - GBufferEffect integrated + HOWTO playbook

- Wire GBufferEffect into demo build: assets.txt, DemoSourceLists.cmake,
  demo_effects.h, shaders.h/cc. ShaderComposer::Compose() applied to
  gbuf_raster.wgsl (resolves #include "common_uniforms").
- Add GBufferEffect construction test. 35/35 passing.
- Write cnn_v3/docs/HOWTO.md: G-buffer wiring, training data prep,
  training plan, per-pixel validation workflow, phase status table,
  troubleshooting guide.
- Add project hooks: remind to update HOWTO.md on cnn_v3/ edits;
  warn on direct str_view(*_wgsl) usage bypassing ShaderComposer.
- Update PROJECT_CONTEXT.md and TODO.md: Phase 1 done,
  Phase 3 (WGSL U-Net shaders) is next active.

handoff(Gemini): CNN v3 Phase 3 is next - WGSL enc/dec/bottleneck/FiLM
shaders in cnn_v3/shaders/. See cnn_v3/docs/CNN_V3.md Architecture
section and cnn_v3/docs/HOWTO.md section 3 for spec. GBufferEffect
outputs feat_tex0 + feat_tex1 (rgba32uint, 20ch, 32 bytes/pixel).
C++ CNNv3Effect (Phase 4) takes those as input nodes.

1 files changed, 18 insertions, 1 deletions

diff --git a/.claude/settings.json b/.claude/settings.json
index fb6efa5..40c1320 100644
--- a/.claude/settings.json
+++ b/.claude/settings.json
@@ -1,3 +1,20 @@
 {
-  "permissions": {}
+  "permissions": {},
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Write|Edit",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "f=$(jq -r '.tool_input.file_path'); if echo \"$f\" | grep -q 'cnn_v3/' && ! echo \"$f\" | grep -q 'cnn_v3/docs/HOWTO.md'; then echo '{\"systemMessage\": \"Reminder: update cnn_v3/docs/HOWTO.md if this change affects the pipeline.\"}'; fi"
+          },
+          {
+            "type": "command",
+            "command": "f=$(jq -r '.tool_input.file_path'); if echo \"$f\" | grep -qE '\\.(cc|h)$' && grep -qE 'str_view\\([a-zA-Z_]+_wgsl\\b' \"$f\" 2>/dev/null; then echo '{\"systemMessage\": \"Direct .wgsl asset usage detected — wrap with ShaderComposer::Get().Compose() before passing to str_view().\"}'; fi"
+          }
+        ]
+      }
+    ]
+  }
 }