Regenerated for the stream record envelope.

[moetemp]

This PR regenerates the Go code for the stream record envelope.

What changed?

• proto/api moves to the record envelope commit on the moetemp/api fork.
• Everything else is what the pin forces: the new stream/v1 package with StreamRecord and StreamRecordKind.
• The payload visitor in proxy/interceptor.go gets a StreamRecord case for body and metadata. Nothing reaches it yet, so no visitor count moves.

Part of AI-198 (epic AI-37).

Why?

It's the Go half of the envelope api PR. Go code that reads or writes stream records through a provider needs the type. Nothing here is hand-written.

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

Same generator run and plugin versions as the channel PRs. make check, go build ./... and go test -tags protolegacy ./... pass. go vet passes everywhere except internal/protojson, which fails the same way on main.

[moetemp]

Replaced by #6 in the v5 series (phase 1, Signal wake only). The branch stays as a pin.