fix(render3d): nothing draws into a BC7 texture - sampler binding binds, and compressed images get no mips

Metal aborted a net.sh guest ("MTLPixelFormatBC7_RGBAUnorm is not color renderable"): the crash
report's main thread was in vkQueueSubmit from gvk_once_end, MoltenVK encoding a vkCmdBlitImage
through a render pipeline. water.ludic bound its reflection by sampler name and then asked the
BOUND texture for mips - on Vulkan the bound texture was not the reflection but the last one
bound, since 23.3 a BC7 kit texture. gpu_bind_sampler now makes its texture the bound one, as
OpenGL did (and water binds it explicitly); gvk_tex_mips and gvk_mips_now skip compressed images;
gvk_pass_begin leaves out a compressed colour attachment and says so.

tests/net.sh passes (main e515bd87 built against it; host and guest agree on 196 animals, the
people, the board and the lost hiker).

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

packages/ludic.render3d/env.ludic

@@ -200,6 +200,7 @@ export state Render3dState {
   gvk_labels: bool = false          # R3D_VK_LABELS: each profiled pass is a debug label (Metal System Trace)
   gvk_inflight: int = -1
   gvk_nopool: bool = false
+  gvk_bc_said: int = 0              # attachments refused for being compressed, said so far
   gvk_has_bc: bool = false          # textureCompressionBC: .dds textures are uploaded compressed
   # R3D_VK_PROF: Vulkan objects made and destroyed, reported every 120 frames
   gvk_mk_img: int = 0