Phase 9: Iris and Complementary Reimagined, off by default

Adrian, 2026-11-09: set up the shader but keep it disabled by default. Iris
1.8.14-beta.1 (built for the pack's Sodium 0.8.13) and Complementary Reimagined
r5.9.3, both client only and fetched from Modrinth. Default Options' extra
folder ships config/iris.properties with shaders off and Complementary
preselected, copied only when a player has none. Toggle Shaders is on M, the
only free letter; Iris's other keys are unbound. tools/build.py fails if the
settings name a shader file the pack doesn't install.

Smoke test passes; client dependencies are satisfied. Not launched on a client.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -11,6 +11,7 @@ A free NeoForge 1.21.1 modpack on Cobblemon 1.8: one large island with soft-gate
 - **Quality of life:** JEI, Jade, Inventory Profiles Next, Mouse Tweaks, AppleSkin, Controlling, Xaero's Minimap and World Map; Default Options ships conflict-free default keybinds (`pack/config/defaultoptions/keybindings.txt`, check with `tools/check_keybinds.py`).
 - **Rules:** no vanilla mobs (only Pokémon), Nether portals don't form.
 - **Performance:** Sodium, FerriteCore, ModernFix, ImmediatelyFast, Entity Culling.
+- **Shaders:** Iris with Complementary Reimagined, installed but off by default (Toggle Shaders key M, or Video Settings > Shader Packs).
 
 Exact versions and each mod's Cobblemon 1.8 status are in [docs/addon-status.md](docs/addon-status.md).