docs: Fix EFFECT keyword syntax and add automation-friendly workflow

Fix EFFECT keyword format across all documentation and scripts - priority
modifier (+/=/–) is required but was missing from examples.

**Documentation fixes:**
- doc/HOWTO.md: Added missing + to EFFECT example
- doc/RECIPE.md: Added priority modifiers to examples
- tools/shadertoy/README.md: Fixed test path, clarified workflow
- tools/shadertoy/convert_shadertoy.py: Updated output instructions

**New automation guide:**
- doc/EFFECT_WORKFLOW.md: Complete step-by-step checklist for AI agents
  - Exact file paths and line numbers
  - Common issues and fixes
  - Asset ID naming conventions
  - CMakeLists.txt dual-section requirement
  - Test list instructions (post_process_effects vs scene_effects)

**Integration:**
- CLAUDE.md: Added EFFECT_WORKFLOW.md to Tier 2 (always loaded)
- doc/AI_RULES.md: Added "Adding Visual Effects" quick reference
- README.md: Added EFFECT_WORKFLOW.md to documentation list

**CMakeLists.txt:**
- Disabled incomplete cube_sphere_effect.cc (ShaderToy conversion WIP)

**Timeline:**
- Commented out incomplete CubeSphereEffect
- Removed obsolete constructor argument

Fixes #issue-with-effect-syntax

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/doc/AI_RULES.md b/doc/AI_RULES.md
index d18a0cc..1a4ee78 100644
--- a/doc/AI_RULES.md
+++ b/doc/AI_RULES.md
@@ -5,3 +5,22 @@
 - Prefer small, reviewable commits
 - All `cmake --build` commands must use the `-j4` option for parallel building.
 - after a task, a 'big' final commit should contain a short handoff tag like "handoff(Gemini):..." if you're gemini-cli, or "handoff(Claude): ..." if you're claude-code.
+
+## Adding Visual Effects
+
+**IMPORTANT:** When adding new visual effects, follow the complete workflow in `doc/EFFECT_WORKFLOW.md`.
+
+**Required steps (must complete ALL):**
+1. Create effect files (.h, .cc, .wgsl)
+2. Add shader to `workspaces/main/assets.txt`
+3. Add `.cc` to CMakeLists.txt GPU_SOURCES (BOTH sections: headless and normal)
+4. Include header in `src/gpu/demo_effects.h`
+5. Add to timeline with `EFFECT +` (priority modifier is REQUIRED)
+6. Add to test list in `src/tests/gpu/test_demo_effects.cc`
+7. Build and verify: `cmake --build build -j4 && cd build && ./test_demo_effects`
+
+**Common mistakes to avoid:**
+- Missing priority modifier in timeline (`EFFECT` must be `EFFECT +`, `EFFECT =`, or `EFFECT -`)
+- Adding `.cc` to only one CMakeLists.txt section (need BOTH headless and normal)
+- Wrong asset ID (check assets.txt entry name → `ASSET_SHADER_<NAME>`)
+- Forgetting to add to test file