fix(installer): honest progress + runnable remedies for WSL GPU setup (#415)

[shujaatTracebloc]

Closes#415.

Problem

On a GPU machine the NVIDIA container toolkit setup inside WSL2 ran entirely through Log (which writes to the log file only), so the console sat blank through the 30s WSL probe, the multi-hundred-MB Ubuntu install, and the 180s toolkit install. On timeout it printed a vague "You can set it up manually inside WSL later" / "GPU setup may need manual attention" with no actual commands.

Fix

• Wait-JobWithProgress — waits on a background job with a spinner + elapsed / timeout heartbeat, bounded, stops the job best-effort on timeout. Every long GPU sub-step (WSL probe, Ubuntu install, toolkit install, verify) now goes through it, so no window is silent for more than ~2s.
• Show-GpuManualRemedy — prints copy-pastable remedy commands (mirroring the in-WSL steps, carrying the same --tlsv1.2 --connect-timeout 30 --max-time 30 floor as the automated path) and a tracebloc doctor follow-up. Called on every timeout/failure branch.
• The Ubuntu install is now a progress-tracked job instead of a silent cmd /c "wsl --install -d Ubuntu" | Out-Null.
• Visible Info intro (optional; CPU mode works either way) + Ok on success; the vague dead-end copy is gone.
• Extracted the shared braille spinner into $script:SpinnerFrames (reused by Wait-ProcessWithDeadline).

GPU setup stays in Step 1 (before New-K3dCluster) because the --gpus flag must be decided there; moving it post-install would force cluster recreation — the exact churn #431 warns about. It remains non-fatal, so CPU mode always completes cleanly.

Acceptance criteria

• No silent window >10s during GPU setup (heartbeat every 2s + visible intro)
• Timeout/failure output contains runnable remedy commands (+ tracebloc doctor)
• Non-blocking consideration addressed (already non-fatal; rationale for staying in Step 1 documented)

Tests

11 new Pester tests (Wait-JobWithProgress, Show-GpuManualRemedy, Install-NvidiaContainerToolkit).

Verified locally (CI-identical):

• Pester full suite: 186 passed, 0 failed, 8 skipped (Windows-only)
• PSScriptAnalyzer: 0 Error-severity
• check-style.sh: clean
• manifest verification: ✔

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Note

Low Risk
Installer-only UX and error messaging for best-effort GPU setup; behavior remains non-fatal with CPU fallback, covered by new Pester tests.

Overview
Improves Windows installer UX for optional NVIDIA container toolkit setup in WSL2 (#415): long steps no longer leave the console silent, and failures print actionable recovery steps instead of vague hints.

Wait-JobWithProgress polls background jobs with a shared braille spinner and elapsed / timeout line (~2s heartbeat), stops the job on timeout, and replaces bare Wait-Job for WSL list, Ubuntu install, toolkit install, and verify. Spinner frames move to $script:SpinnerFrames (also used by Wait-ProcessWithDeadline).

Show-GpuManualRemedy prints copy-pastable WSL commands (matching the automated path) plus tracebloc doctor on timeout/failure branches. Ubuntu install runs in a progress-tracked job (600s cap) instead of silent cmd /c | Out-Null. Visible Info/Ok lines replace log-only progress; GPU setup stays non-fatal (CPU fallback).

Pester tests lock the new helpers and GPU flow contracts; manifest.sha256 updated for install-k8s.ps1.

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