feat(render3d): 23.3 - a .dds beside a .png is uploaded BC-compressed with its whole mip chain

The device's textureCompressionBC is asked for and remembered (gvk_has_bc). tex_load_ex prefers a
DX10 .dds with the full chain beside the .png (not for an edge-padded cut-out atlas):
texture_dds.ludic reads BC7 / BC5 / BC4, gpu_tex_compressed makes the image with every level and
no colour-attachment use (a compressed image is only sampled and copied into), and
gvk_tex_upload_blocks copies each level's blocks from one staging buffer. A colour map is BC7
sampled as sRGB, a data map BC7 read as it is. examples/rendering/bc.ludic holds it, in the suite;
ludic.lab's plate carries its .dds (its three shots render at 56-60 dB against the .png's).

ludic-dev test 307/307, no Vulkan SDK in the environment.

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_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
   gvk_mk_view: int = 0