AGENTS: add FULL 3D DESKTOP non-negotiable policy; qtbase: add mesa/libdrm/libepoxy deps + EGL/GLES feature flags

- Mandatory 3D desktop policy: no disabling OpenGL/EGL as workaround
- Mesa build requirements documented (drivers, flags, ioccom stub)
- qtbase: added mesa/libdrm/libepoxy to build dependencies
- qtbase: added -DQT_FEATURE_opengles2=ON -DQT_FEATURE_egl=ON
  to override cmake auto-detection for cross-compilation
- Mandatory package list: mesa, libdrm, libepoxy, redox-drm,
  qtbase, qtdeclarative, qtwayland, kwin, sddm

local/recipes/qt/qtbase/recipe.toml

@@ -19,6 +19,9 @@ dependencies = [
     "zlib",
     "libwayland",
     "dbus",
+    "mesa",
+    "libdrm",
+    "libepoxy",
 ]
 script = """
 DYNAMIC_INIT