Mesh particles render with all UVs collapsed to zero when the Mesh's TexCoord channel uses an integer vertex format, while the same Mesh on a MeshRenderer renders correctly

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Copy the attached "MeshParticleTexcoordReproWindow.cs" into the project's "Assets/Editor" folder and let it import
3. Open Window > QA > Mesh Particle Texcoord Format
4. Press "Set up repro"
5. Observe the two quads in the Game view - the left one is the Particle System, the right one is the MeshRenderer
6. Press "B. Float32x2 UVs + Sprites/Default"
7. Observe the two quads again
8. Press "C. UInt16x2 UVs + Particles/Unlit, inst ON" and then "D. UInt16x2 UVs + Particles/Unlit, inst OFF"
9. Observe the two quads after each press
10. Press "Enable Texture Sheet Animation (2x2 tiles)" and observe the particle with each of the two Meshes assigned

Actual results: At step 5 the Particle System's quad renders as a single flat colour - the texel at UV (0,0) because every texcoord reads as approximately zero, while the MeshRenderer's quad renders the texture's four colours correctly from the same Mesh asset. Measured off-screen at 64x64, the particle covers 1764 pixels of one colour where the correct result is 441 pixels each of four colours, which is what the MeshRenderer produces. At step 7 the particle matches the MeshRenderer exactly; the only difference between the two Meshes is the TexCoord0 storage format.

Expected results: Mesh particles use the Mesh's texcoord data as authored, so a Particle System in Mesh render mode and a MeshRenderer render the same Mesh identically regardless of the TexCoord channel's storage format 

Reproducible with versions: 6000.0.0f1, 6000.0.84f1, 6000.3.24f1, 6000.6.2f1, 6000.7.0b1, 7000.0.0a1

Tested on (OS): MacOS Silicon Tahoe 26.6.2