feat(render): shader ABI v2 - AtmosphericFrame gains clock/wind blocks; caster pass binds it (Campaign VM VM6a)

AtmosphericFrame (set 3/binding 5) grows additively from 160 to 192 bytes:
two appended vec4 members, uAtmosphereClockWind and uAtmosphereWindAmplitude,
carry the foliage-wind clock/weather and amplitude inputs VM6b's shader
displacement will read. RenderPackShaderAbi renames the old constant to
AtmosphericFrameSizeBytesV1 (160), adds AtmosphericFrameSizeBytesV2 (192),
keeps AtmosphericFrameSizeBytes pointing at the current (v2) size, and adds
ShaderAbiVersion = 2. RenderPackSpirvValidator.ValidateAtmosphericFrame
accepts either the v1 (seven-member, 160-byte) or v2 (nine-member, 192-byte)
shape and rejects anything else naming both — this is why the frozen
external sample packs under samples/*/Shaders/*.spv, whose GLSL sources are
not in this tree, need no rebuild: a v1 shader bound to the 192-byte buffer
still reads correctly, since a bound range only needs to be >= the block's
own declared size.

DirectionalSunShadowRenderer's caster pass now binds AtmosphericFrame too
(both the multiview and per-cascade sites), through a new
AtmosphericFrameBufferBinding the graph owns and supplies via
DirectionalSunShadowRenderInput. AtmosphericPostProcessGraph.RenderDirectionalShadows
builds its own 192-byte ring allocation for this, separate from the world
receiver's frame block, because the caster pass runs before RenderPostProcess
constructs that block within the same frame. The four world caster pipeline
variants (opaque/cutout, base/multiview) are now allowed to declare binding
5 in the validator; terrain casters are untouched.

This commit is plumbing only: the two new members are always written but
never read by any shader yet (zero placeholders), so pack-on and pack-off
output are both pixel-identical to before. VM6b wires the real weather-driven
values and the shader-side displacement.

App hermetic filter: 5972/5974 (2 pre-existing failures unrelated to this
change, confirmed against the unmodified baseline). Core.Tests hermetic:
4697/4697. RenderPackValidator.Tests: 30/30. VulkanShaderManifestTests
(retail oracle set): 7/7, byte-identical.

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

docs/render-packs/README.md

@@ -209,6 +209,15 @@ optional after a pass unconditionally declares them.
   these graphics declarations. Additive enum/record support stays compatible;
   a breaking contract requires a new render-pack API version and explicit
   compatibility path.
+- `RenderPackShaderAbi.ShaderAbiVersion` separately versions the numeric
+  SPIR-V interface (set/binding numbers and std140 block layouts) declarations
+  are validated against — distinct from `RenderPackApi`/`PluginApi`. Campaign
+  VM VM6 shipped v2: `AtmosphericFrame` (set 3, binding 5) grew additively
+  from 160 to 192 bytes (see `docs/render-packs/semantic-bindings-v1.md`'s
+  "ABI v2 (additive)" section). `RenderPackSpirvValidator` accepts both the
+  v1 and v2 shapes, so shader assets compiled before a version bump — the
+  external sample packs among them — never need a rebuild for an additive
+  change.
 - Persisted identity is pack ID + pack version + preset ID, never list index.
   User-authored setting strings are keyed by the same stable pack identity and
   stable setting ID, never declaration or menu index.

docs/render-packs/semantic-bindings-v1.md

@@ -87,7 +87,7 @@ checked-in shared render-pack GLSL includes are the byte-offset SSOT; authors
 include those definitions rather than maintaining a private copy. The tables
 below state the same values for review and tool diagnostics.
 
-### `AtmosphericFrame` — set 3, binding 5, 160 bytes
+### `AtmosphericFrame` — set 3, binding 5, 192 bytes (ABI v2; see below)
 
 ```glsl
 layout(std140, set = 3, binding = 5) uniform AtmosphericFrame {
@@ -134,6 +134,38 @@ curve without an exact 0-degree point must make its first positive point zero.
 from scene depth and the normalized viewport coordinates. Matrix convention
 and depth range match the shared push-block `viewProjection`.
 
+### ABI v2 (additive) — Campaign VM VM6
+
+`AtmosphericFrame` grew from 160 to 192 bytes by appending two members after
+`uAtmosphereInverseViewProjection`. Nothing above this line moved or changed
+meaning:
+
+```glsl
+layout(std140, set = 3, binding = 5) uniform AtmosphericFrame {
+    // ... the seven v1 members, unchanged ...
+    vec4 uAtmosphereClockWind;     // @160: elapsed seconds, wind mean [0..1], wind gust [0..1], wind direction radians
+    vec4 uAtmosphereWindAmplitude; // @176: lean amplitude m, branch amplitude m, flutter amplitude m, max canopy height m
+};
+```
+
+`uAtmosphereClockWind`/`uAtmosphereWindAmplitude` feed the shared
+`foliage_wind.glsl` include, which `mesh_atmospheric.vert` and the four
+`directional_shadow_world_*` (opaque/cutout, base and multiview) caster
+vertex shaders call identically so a displaced leaf's shadow moves with it.
+No other pass reads these members.
+
+**Compatibility rule:** the host always allocates and binds the full 192-byte
+v2 block (`RenderPackShaderAbi.AtmosphericFrameSizeBytes`), but a v1 shader —
+one compiled before this campaign, declaring only the original seven members
+— binds and reads correctly against it: a bound range only needs to be at
+least as large as the block's declared size, so the shader simply never sees
+the appended bytes. `RenderPackSpirvValidator.ValidateAtmosphericFrame`
+accepts either the v1 shape (seven members, 160 bytes) or the v2 shape (nine
+members, 192 bytes); any other member count is rejected naming both. This is
+why the external sample packs under `samples/*/Shaders/*.spv` — whose GLSL
+sources are not in this tree and are never recompiled — needed no rebuild for
+this change.
+
 ### Colour space
 
 The main-world colour target, `uAtmosphereSunColor` (sun-ray input), and any