T36's op gate is not registered in tests/CMakeLists.txt, so it has never been built or run

Row: GFX1100-TG200

#2891 adds tests/vt/test_rocm_prefill_tile.cpp as T36's op-level gate. It adds
no entry for it in tests/CMakeLists.txt, so no target exists:

$ ninja -C build test_rocm_prefill_tile
ninja: error: unknown target 'test_rocm_prefill_tile'

Two documents in the same change say it runs:

• .agents/specs/gfx1100-tg200.md:223 -- "op gate
  tests/vt/test_rocm_prefill_tile.cpp"
• docs/bench-evidence/gfx1100-tg200-t36-prefill-mtile-20260829.md:27 --
  "tests/vt/test_rocm_prefill_tile.cpp (registered test_rocm_prefill_tile)"

It is not registered. The file is never compiled and never executed, so T36's
BIT-IDENTICAL claim -- the whole reason the arm is allowed to be adopted -- has
no gate behind it in this tree. ctest -R 'rocm|quant' cannot see it either.

Nothing about the T36 kernel itself is in question here; only that the test
asserting it is inert.

Found while gating the external-contributor ROCm stack on strix:gpu0. Fixed in
the same flow on #2891's branch by registering the target beside
test_rocm_quant_dot.

Start with tests/CMakeLists.txt and compare the missing test with the nearby test_rocm_quant_dot registration. Check tests/vt/test_rocm_prefill_tile.cpp and verify that the target builds with ninja, runs under ctest -R 'rocm|quant', and is no longer absent from the test list.