fix: blento URLs, parallel search prefetch, tpuf keepalive
- skip blento.app base_paths in URL construction (blento is a card
portal, not a document server) — affected docs fall through to
leaflet.pub/p/{did}/{rkey} or platform-specific fallbacks
- prefetch search API call in parallel with atlas.json when ?q= is
present, eliminating stacked latency on shared links
- add 3-minute tpuf keepalive ping to prevent cold start penalty
(~600-900ms extra on first query after inactivity)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>