Prefer NCU details in profiler output

[msaroufim]

Summary

Makes Nsight Compute details the default profiler artifact surfaced by popcorn-cli --profile-brev:

• downloads and extracts ncu-details.txt
• downloads and extracts ncu-details.csv
• still downloads/extracts profile.ncu-rep when present
• prints details links first
• keeps the open -a "NVIDIA Nsight Compute" ... command as the final line for the optional GUI report

Behavior

For QR v2 benchmark index 0, the CLI output now includes local links like:

NCU details for agents: profile.0-batch-20-n-32-cond-1-seed-43214/ncu-details.csv
NCU details for agents: profile.0-batch-20-n-32-cond-1-seed-43214/ncu-details.txt
Open in Nsight Compute: profile.0-batch-20-n-32-cond-1-seed-43214/profile.ncu-rep
open -a "NVIDIA Nsight Compute" 'profile.0-batch-20-n-32-cond-1-seed-43214/profile.ncu-rep'

The .ncu-rep remains useful for the desktop app, but the text/CSV details are the intended default for agents and terminal workflows.

Validation

• cargo fmt --check
• cargo test
• End-to-end QR v2 profile through the hosted service:

POPCORN_BREV_PROFILER_URL=https://http--brev-profiler-proxy--dxfjds728w5v.code.run \
  cargo run -- submit /Users/mark/Dev/reference-kernels/problems/linalg/qr_v2/submission.py \
  --leaderboard qr_v2 \
  --profile-brev \
  --benchmark-index 0 \
  --no-tui

The run produced:

• profile.0-batch-20-n-32-cond-1-seed-43214/ncu-details.txt
• profile.0-batch-20-n-32-cond-1-seed-43214/ncu-details.csv
• profile.0-batch-20-n-32-cond-1-seed-43214/profile.ncu-rep

Notes

No kernelbot or kernelboard changes are included.