Kudzu 0.8.52 - Effect-private mutable refs

Kudzu 0.8.52 lowers top-level useRef(null) and useRef(0) values into invocation-private closures when one inline effect exclusively owns every direct .current reference and cleanup. E2B terminal and WebSocket fixtures now preserve generation invalidation, dependency replacement, BFCache retention, listener removal, stale callback rejection, and exact close behavior without serialized ref captures, ResourceIR, or a resource runtime. JSX DOM refs remain component-owned, while aliases, nonzero initializers, cross-effect/event use, missing cleanup invalidation, and escaped ref objects remain source-diagnosed.