hardened bluesky app fork with microcosm

microcosm Phase 0-2: clients, Slingshot record reads, Constellation interaction counts master

- Add src/lib/microcosm/ typed clients (constellation, slingshot, spacedust) with env hosts and a MICROCOSM_ENABLED flag - Route threadgate/postgate record reads through Slingshot (PDS fallback) - Add Constellation-backed react-query hooks (counts + distinct-DID lists) - Surface a live network-wide like count on the focused thread post - Add MICROCOSM_PLAN.md and the three verified OpenAPI specs