docs: remove specs/

Clear out the specs directory — mostly stale (S-52 portrayal engine, CSP
completeness, the now-complete S-52→S-101 migration tracking) or superseded
planning docs. Code is the source of truth; live plans (NMEA, profiles) live in
the issue tracker / memory.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: beetlebugorg