Regenerated for the notification channel service.

[moetemp]

This PR regenerates the Go code for the notification channel service.

What changed?

• proto/api points at the channel service commit on the moetemp/api fork, so .gitmodules names the fork until the api change lands upstream.
• Everything else is what the pin forces: the new notification/v1 package, the five RPCs in the gRPC, gateway, proxy and mock code, and temporalproto/openapi.
• proxy/request_header.go sets temporal-resource-id to channel:<name> on the five requests.
• The payload visitor in proxy/interceptor.go walks Notification.metadata, so a codec reaches it on notify, poll and describe.

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

Why?

It's the Go half of the channel service api PR. Nothing here is hand-written.

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

I ran the make proto generator targets. A regen at the upstream api commit reproduces main with no diff, so the plugin versions match. nexus-rpc-gen isn't installed locally, but the Nexus inputs don't change, so the committed file stays. 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]

Paused per the 2026-10-05 design review (the decision record is on the proposal page, section 14). Resumes in phase 2 with the CHASM notification work. The branch stays as a pin.