Hide in-explorer-redundant CTAs, add copy-link chip everywhere in /explore master
Two changes: * RecordPreview gets a hideExplorerCtas prop that suppresses the \"View Full Record\" JSON-modal button and the \"Open in Explorer — backlinks, identity, raw JSON →\" cross-link. RichRecordPreview passes it: inside the record explorer the linkified raw JSON is already rendered inline immediately below, and the page itself IS the Explorer destination, so both CTAs were noise. Universal link pages keep them. * New ShareLinkChip — small \"Copy link\" button rendered at the end of every explore page. Repos and records copy their universal link (aturi.to/<handle> and aturi.to/<handle>/<col>/<rkey>), so the pasted URL drops into any compatible Atmosphere client via the WaypointPicker. Collection pages copy the explore URL (no universal route exists for them). PDS pages copy aturi.to/explore/pds/<host>. The chip lives in the Breadcrumb's right-side gap for repo/collection/record pages and inside the PDS card header for the PDS page.