docs(contributing): restore Palimpsest framework reference (#223)

Owner directive 2026-06-02: Palimpsest functions as both legal licence
(only palimpsest / palimpsest-plasma / consent-aware-http) AND ethical
framework reference across the estate. Doc-maxout #182 erased the
framework half along with stale dual-licence claims; this restores the
framework mention. SPDX/legal licence (MPL-2.0) unchanged.

Manual edit per owner directive — single-file, per-file approved.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath