* fix(setup): support classic piped quick installation

Add a bounded in-memory bootstrap that restores controlling-terminal input for CLI and restart prompts, rejects incomplete downloads, and supports headless flags. Preserve the standalone updater and source-checkout installer.

Document the one-line command and inspection flow. Cover the exact pipeline under a controlling PTY, sh, POSIX mode and headless execution plus truncation and error propagation. Documentation: reconcile README, Development and Unreleased; managed CLI usage and parity TODO remain unchanged. Reviewed with Opus 5.5 medium and Gemini 4 Argon medium.

* fix(setup): bound bootstrap fetch and document reliable scripted status

Keep the requested classic interactive pipeline, restore connection/transfer/size/redirect bounds, and provide a Bash pipefail command for unattended scripts. Document the interactive pipeline's empty-download exit-status limit.

Run both README commands from sh and cover DNS/HTTP/timeout/size failure codes, installer failure propagation and first-request bounds. Documentation: reconcile README, Development and Unreleased; parity TODO remains unaffected. Addresses PR #542 review feedback.

* fix(setup): keep README bootstrap fetch bounded under pipefail

Propagate curl failures from the documented quick-install pipeline and restore
HTTPS, time, size, and redirect limits on the bootstrap download. Cover both
with release-setup regressions.