QVAC-23083 infra[skiplog]: use self-hosted GPU runner for Snap E2E

[Victor-Rodzko]

🎯 What problem does this PR solve?

• Manual Snap SDK E2E runs default to a CPU-only GitHub-hosted runner even though the dedicated GPU runner is now provisioned.
• Persistent global temporary files on a self-hosted runner can block Electron packaging across CI runs.

📝 How does it solve it?

• Uses qvac-ubuntu2204-x64-gpu as the default Snap runner for workflow dispatches and reusable-workflow fallback resolution.
• Keeps snap-platforms configurable so callers can still override the runner explicitly.
• Isolates both Snap revision builds under the runner-owned temporary directory instead of shared /tmp state.

🧪 How was it tested?

• Validated both modified workflows with actionlint.
• Verified both the dispatch default and job fallback resolve to qvac-ubuntu2204-x64-gpu.
• Verified both Snap revision builds receive TMPDIR: ${{ runner.temp }}.
• Launched a full Snap E2E rerun from the updated branch.

[github-actions]

License compliance — clean

No new dependency license findings in this PR.

Warn-only (shadow) mode — this check does not block merges yet.

Updated automatically by the canonical license compliance workflow.

NOTICE presence (advisory)

Missing NOTICE (advisory, does not block):

• ./.github/actions/release-merge-guard
• ./docs/website
• ./packages/ggml-coload-smoke
• ./packages/fabric/test/integration
• ./packages/inference-addon-cpp/mobile
• ./packages/sdk/e2e
• ./packages/llm-llamacpp/benchmarks/performance
• ./packages/llm-llamacpp/benchmarks/server
• ./packages/vla-ggml/sim/server
• ./packages/embed-llamacpp/benchmarks/performance
• ./packages/embed-llamacpp/benchmarks/server
• ./packages/asr-ggml/benchmarks/server

[github-actions]

Workflow security (shadow mode)

zizmor found 1115 finding(s) in .github/ (highest severity: high). This check is warn-only and does not block the merge.

Findings are annotated inline on the changed files and listed in the job summary.

Reproduce locally:

pipx run zizmor==1.27.0 --offline .github/