feat: add rgt rig sync to backfill existing rigs into registry

feat: re-register rigs from rigs.toml on rgt start

feat: rig workflow uses Continue-As-New on stop, tracks session IDs

feat: add session ID fields to RigState

feat: persist rig to rigs.toml on add

feat: add resume_session_id to SpawnAgentInput for Claude --resume

feat: add discover_session_id activity for Claude session tracking

feat: add RigsConfig load/save/add/remove helpers

fix: remove stale symlink/binary before cp in install.sh

fix: use /tmp for temp dir and remove EXIT trap in install.sh

fix: create /usr/local/bin if it doesn't exist before installing

fix: vendor OpenSSL to fix x86_64-apple-darwin cross-compilation

ci: fix macOS x86_64 cross-compilation — set OPENSSL_STATIC=1

ci: install protoc before cargo build — required by prost-wkt-types

docs: update README install instructions — curl pipe installer