PowerShell-first install and provider-switching guidance was missing from the release-readiness path, so add a focused quickstart and link it from the primary docs without touching runtime code.
Constraint: G009 task 4 scope is docs-only install/release quickstart and provider switching; do not mutate .omx/ultragoal.
Rejected: Runtime or installer changes | task asks for command-copyable docs and source-of-truth alignment, not product behavior changes.
Confidence: high
Scope-risk: narrow
Directive: Keep Windows examples placeholder-secret only and prefer explicit provider model prefixes when multiple credentials may exist.
Tested: cargo fmt --check; cargo check --workspace; cargo clippy --workspace --no-deps; markdown link/fence/grep validation.
Not-tested: cargo test --workspace has pre-existing failing rusty-claude-cli::tests::session_lifecycle_prefers_running_process_over_idle_shell unrelated to docs; targeted rerun reproduces.
Co-authored-by: OmX <omx@oh-my-codex.dev>
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