feat(render3d): load steps for a loading screen, four quality switches, and the ring's uniform usage

- r3d_open opens the window with nothing baked; r3d_load_count / r3d_load_step run the rest (sky
  and light, terrain, shadow and screen targets, cover and actors, grass) so a game can present a
  loading frame between them. r3d_init is the same calls in a row.
- sky_set_quality(width): the prefiltered sky light at 256 / 512 / 1024, baked again.
- post_set_msaa(samples): multisampling on OpenGL, remade in place (post_msaa_live is false on
  Vulkan); post_free frees the multisampled framebuffer too.
- STREAM_BUDGET_US is a variable; r3d_fog_scale multiplies the fog the day sets.
- Vulkan buffers carry UNIFORM_BUFFER usage: the frame's ring is bound as uniform buffers and was
  created without it (VUID-VkWriteDescriptorSet-descriptorType-00330, found on MoltenVK).

OpenGL frames at the five viewpoints unchanged; the game's 59 self-tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/ludic.render3d/gpu_vk_res.ludic

@@ -585,7 +585,7 @@ function gvk_buf_reserve(b: int, n: int) -> bool {
   Vk.zero(bci, VkBufferCreateInfo_sizeof)
   Vk.put_i32(bci, VkBufferCreateInfo_sType, VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO)
   Vk.put_i64(bci, VkBufferCreateInfo_size, size_l)
-  Vk.put_i32(bci, VkBufferCreateInfo_usage, VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_INDEX_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_INDIRECT_BUFFER_BIT)
+  Vk.put_i32(bci, VkBufferCreateInfo_usage, VK_BUFFER_USAGE_VERTEX_BUFFER_BIT | VK_BUFFER_USAGE_INDEX_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT | VK_BUFFER_USAGE_STORAGE_BUFFER_BIT | VK_BUFFER_USAGE_INDIRECT_BUFFER_BIT | VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT)
   Vk.put_i32(bci, VkBufferCreateInfo_sharingMode, VK_SHARING_MODE_EXCLUSIVE)
   let out = bytes(8)
   var r = Vk.create_buffer(gvk_dev, bci, null, out)