fix: pure node stream PPR resume path, avoid Readable.toWeb() interop
Readable.toWeb() produces streams with Node-internal state that breaks
when mixed with web TransformStreams during cancellation. Instead of
bridging through web streams, construct the PPR resume response as a
pure Node Readable chain: cached HTML (Readable.from) + sentinel +
PassThrough bridge, joined via chainNodeStreams. The resume render
pipes to the bridge via pipeToNodeWritable (node:stream/promises
pipeline). Web TransformStream path kept for non-node-streams builds.