Align CLI docs with one cache interface

[gauravtiwari]

What changed

• replaces internal proxy setup guidance with the normal tool-named adapters
• removes the retired proxy-mode page
• aligns onboarding, archive, Action, installer, and tool documentation around one committed repo plan

Why

Customers should use the same small CLI-owned interface locally and in CI. Internal helper commands are implementation plumbing, not a second setup path.

Checks

• exact public distribution alignment check
• forbidden public marker scan
• installer trust tests
• Markdown whitespace validation