fix(render): jitter the volumetric march per pixel (IGN); file #421 for the shadow transform buffer (Campaign VM VM5)

Fixed step-count volumetric ray marches (Low/Medium presets, e.g. 40 steps)
sample the same t values at every pixel, so a shadow-cascade edge crossing
lands at the same march step across a whole neighbourhood of pixels and
reads as visible concentric banding around light shafts. Offset each
pixel's march phase with interleaved gradient noise (Jimenez 2014,
fract(52.9829189 * fract(dot(gl_FragCoord.xy, vec2(0.06711056,
0.00583715))))) instead of the fixed 0.5 sub-step center: t = (step + ign)
/ steps. This decorrelates the step boundaries across pixels, turning the
banding into fine per-pixel noise that the existing quarter/half-res
upsample already averages away. Pack-on only — atmospheric_volumetric is
never used on the retail default path; extinction, colour, and early-outs
are unchanged.

Regenerated SPIR-V via tools/compile-shaders.ps1: only
atmospheric_volumetric.frag.spv and shaders.manifest.json's source hash
for that stage changed.

Also files #421 (docs/ISSUES.md) for Campaign AR review finding F7: the
directional-shadow pass's DirectionalShadowTransformBufferSet duplicates
the main pass's N.5 instance SSBO instead of binding it, to be resolved
once the planned GPU-culling step for shadow cascades lands. Updates the
VM5 ledger row and outcome note in
docs/plans/2026-08-22-visualmaster-campaign.md.

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

src/AcDream.App/Rendering/Shaders/spv/shaders.manifest.json

@@ -92,7 +92,7 @@
         },
         {
           "stage": "frag",
-          "sourceSha256": "8d6177707a95cf0230881bbfb7467c0591632eb67dce3c758596c83cafb14ffc",
+          "sourceSha256": "0195fa5fdfb3850e090bed6f144981d454edfed526b79efe8dd5300b610b2f0f",
           "compiled": true
         }
       ]