Fix website guide pages so they respect the selected CLI or PowerShell surface consistently.

[stiwicourage]

Summary

Fix website guide pages so they respect the selected CLI or PowerShell surface consistently.

Problem

Several docs/*.html pages mix CLI and PowerShell guidance in ways that do not consistently honor the selected command surface. Some pages remain PowerShell-first even when a command-line alternative exists, and some always-visible notes mix both surfaces instead of letting the toggle control the experience.

Scope

Update these pages:

• docs/getting-started.html
• docs/index.html
• docs/core-workflows.html
• docs/working-with-modules.html
• docs/project-json-reference.html
• docs/troubleshooting.html

Acceptance criteria

• dual-surface pages respect the selected surface consistently
• PowerShell-only steps are clearly marked only when no CLI equivalent exists
• docs/getting-started.html no longer implies that nova resolves after Import-Module
• command-line onboarding clearly shows when Install-NovaCli is required
• always-visible mixed-surface notices are replaced with toggle-driven or clearly scoped guidance
• Invoke-NovaCli is removed from website end-user guidance
• README.md and CHANGELOG.md are reviewed during implementation

Out of scope

• rewriting docs/commands.html
• PlatyPS cleanup
• launcher architecture changes