Add multimodal artifact upload

[kirklandsign]

Summary

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Test plan

[PLEASE REMOVE] How did you test this PR? Please write down any manual commands you used and note down tests that you have written if applicable.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16576

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❗ 1 Active SEVs

There are 1 currently active SEVs. If your PR is affected, please view them below:

• ROCm runners linux.rocm.gpu.gfx942.1.b failing

❌ 5 New Failures, 2 Unrelated Failures

As of commit b62bc41 with merge base cccf977 ():

NEW FAILURES - The following jobs have failed:

• nightly-model-export / export-models-xnnpack (gemma3-1b|xnnpack|--quantize) / linux-job (gh)
  At least one of the pre-conditions you specified did not hold
• nightly-model-export / export-multimodal-models (gemma3-4b) / linux-job (gh)
  At least one of the pre-conditions you specified did not hold
• Test CUDA Builds / test-model-cuda-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t ffda1dcb7dd272eaa0cbcc9da7570b60bedb1ef16b624a3541abc33fe39edb8a /exec failed with exit code 1
• Test Metal Backend / test-model-metal-e2e (mistralai, Voxtral-Mini-3B-2507, non-quantized) / macos-job (gh)
  The process '/usr/bin/git' failed with exit code 128
• Test Metal Backend / test-model-metal-e2e (openai, whisper-large-v3-turbo, non-quantized) / macos-job (gh)
  The process '/usr/bin/git' failed with exit code 1

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-samsung-models-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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