[iterate-3T] Real UV interpolation + per-draw textures: shader/UV/bind chain complete

Build the full texture-sampling chain for the publisher splash so the textured
logo CAN sample real artwork at the guest's real UVs. Measured with an env-gated
frontbuffer readback (since removed): the chain is correct end-to-end, but the
sampled K8888 1280x768 texture is ALL-ZERO in the UI window's reachable boot
range — the artwork is produced by an EDRAM resolve (RT->texture copy) that ours
does not yet perform (resolves=0). So this lands the correct shader/UV/bind work
and isolates the remaining blocker to the resolve gap, not the shader path.

Translator (xenia-gpu/src/translator.rs), all UI-translator-only:
- Real Xenos export-index model (replaces the AllocKind heuristic that collapsed
  every VS export to one color slot and DROPPED the texcoord). When export_data
  is set the 6-bit vector_dest IS the export index: VS 62=oPos, 0..15=interps;
  PS 0=RT0. The logo VS exports oPos(62), interp0(color), interp1(UV) distinctly.
- Real interpolator passthrough: VsOut carries 8 interpolator locations; the PS
  seeds r[i] = in.interp[i] (Xenos PS-input-GPR mapping) so tfetch samples at the
  real interpolated texcoord (r1) instead of (0,0).
- vfetch format 6 (k_16_16) packed-16 unpack + per-attribute dword offset, so the
  3 vfetches sharing one fetch-constant (pos/UV/color in a 6-dword vertex) read
  the right attribute. Previously rejected the whole logo VS to the interpreter.
- QuadList/RectangleList host->guest vertex-index remap in the VS (replay is
  non-indexed): QuadList 6 host verts -> guest [0,1,2,0,2,3] (full quad).

fetch.rs: decode vfetch `offset` (dword2[8:15], dwords), `is_signed`,
`is_normalized`.

Per-draw textures: DrawCapture carries the decoded texture(s) (keyed off the
active PS's tfetch slots, attached in gpu_system after decode);
render.rs::dispatch_xenos_captures uploads + binds each capture's texture via the
host texture cache before its draw, instead of one last-draw primary_texture.

Determinism: all changes feed only the UI translator/capture path; frame_captures
is None headless. `check -n50m --gpu-inline --stable-digest --expect` byte-
identical (exit 0). 681 tests pass (+2 regression: logo VS now translates with
interpolators; PS seeds interps into registers). Temp readback/dump probes removed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/xenia-gpu/src/draw_capture.rs

@@ -66,6 +66,13 @@ pub struct DrawCapture {
     /// already carries the render-target → wgpu Y-flip (negated).
     pub ndc_scale: [f32; 2],
     pub ndc_offset: [f32; 2],
+    /// iterate-3T: the decoded texture(s) this draw's active pixel shader
+    /// samples, keyed off its real `tfetch` fetch-constant slots (the 3M
+    /// decoder makes these decode). The UI uploads + binds the FIRST entry
+    /// per-draw so the textured logo samples the real artwork instead of the
+    /// magenta stub. Empty for flat (no-tfetch) draws. Populated by
+    /// `gpu_system` after decode (left empty by `build`).
+    pub textures: Vec<(crate::texture_cache::TextureKey, Vec<u8>)>,
 }
 
 /// iterate-3S: compute the guest→host NDC XY transform for a draw, mirroring
@@ -287,5 +294,6 @@ pub fn build(
         has_real_vertices: has_real,
         ndc_scale,
         ndc_offset,
+        textures: Vec::new(),
     }
 }