Pinned the server and api-go forks to the channel heads.

[moetemp]

This PR pins the server and api forks that serve the notification channel, plus what the pins force.

What changed?

• go.mod replaces go.temporal.io/server with github.com/moetemp/temporal at the top of the channel server chain.
• go.mod replaces go.temporal.io/api with github.com/moetemp/api-go at the channel api head.
• The Go directive moves to 1.27.0, nexus-rpc/sdk-go to v0.7.0 and go.temporal.io/sdk to v1.48.0.

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

Why?

Nothing here is a feature. The channel commands in the next PR need the channel RPCs from the api fork and a server that serves them in start-dev. You can't take the api alone, since the stock server stops compiling once WorkflowServiceClient gains the channel methods. The server fork already requires the newer Go, nexus and sdk, so go mod tidy lifts them with the pin. The require line for the server stays on the tagged release, so the server version check still passes.

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

go build ./... passes on the pins with no CLI change, and go mod tidy leaves both modules as they are. The next PR runs the suites on this pin.

[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.