chore(shipyard): remove apps/shipyard, served from cosscom/coss (#871)

coss.com/shipyard and /shipyard/docs are served by coss.com's site in
cosscom/coss (apps/site), where the landing page and docs were moved
(cosscom/coss#51, #52). This copy was never deployed and would only drift.
The products menu keeps linking to /shipyard.

Claude-Session: https://claude.ai/code/session_018shdXm52pLc2E5HNmFLM44

Author: pumfleet