Clarify forwarding config and avoid duplicating Multi-Cluster Replication

- Split auto-forwarding into its two required parts: the static
  dcRedirectionPolicy (defaults to no redirection) and the per-Namespace
  system.enableNamespaceNotActiveAutoForwarding dynamic config.
- Trim the httpAddress step to the Nexus-specific delta (httpPort + httpAddress)
  and defer base clusterMetadata/rpcAddress setup to the Multi-Cluster
  Replication page it links to.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: stephanos

docs/production-deployment/self-hosted-guide/temporal-nexus.mdx

@@ -112,32 +112,39 @@ target an external URL (`--target-url`), which is experimental and not covered h
    [Nexus Endpoint registry](/nexus/registry) isn't replicated across Clusters.
    Create the same Endpoints (same target Namespace and Task Queue) on each Cluster.
 
-3. **Give every Cluster a frontend HTTP address, set *and* advertised.** Each
-   Cluster must set a local `frontend.rpc.httpPort` and advertise it through
-   `clusterMetadata.clusterInformation.<cluster>.httpAddress`. This is the same
-   `httpAddress` shown in [Enable Nexus](#enable-nexus), but for failover you set it
-   on **every** Cluster, each with its own address. Callback routing resolves this
-   address at delivery time. Without it, cross-Cluster callbacks fail with
+3. **Advertise a frontend HTTP address on every Cluster.** On top of the
+   `clusterMetadata` you configured for replication, each Cluster must set a local
+   `frontend.rpc.httpPort` and add an `httpAddress` to its `clusterInformation`
+   entry so peers can reach it. Callback routing resolves this address at delivery
+   time. Without it, cross-Cluster callbacks fail with
    `HTTPAddress not configured for cluster: <name>`. The `operator cluster upsert`
    command doesn't set `httpAddress`, so configure it explicitly and re-run
    `upsert` after changing it.
 
    ```yaml
-   # cluster-a (repeat on every Cluster with its own addresses)
    services:
      frontend:
        rpc:
          httpPort: 7243
    clusterMetadata:
      clusterInformation:
-       cluster-a:
-         rpcAddress: "cluster-a-host:7233"
-         httpAddress: "cluster-a-host:7243"   # advertised to peers, required
+       cluster-a:                             # existing replication entry, per Cluster
+         httpAddress: "cluster-a-host:7243"   # add this, advertised to peers
    ```
 
-4. **Enable automatic forwarding** (per Namespace) so a request that lands on a
-   standby Cluster forwards to the active one, with the frontend
-   `dcRedirectionPolicy` set to allow redirection (for example, `all-apis-forwarding`).
+4. **Enable automatic forwarding** so a request that lands on a standby Cluster
+   forwards to the active one. This has two parts.
+
+   Set the server's `dcRedirectionPolicy` in static config. It defaults to no
+   redirection, so you must set it to `all-apis-forwarding` (or
+   `selected-apis-forwarding`):
+
+   ```yaml
+   dcRedirectionPolicy:
+     policy: "all-apis-forwarding"
+   ```
+
+   Turn on auto-forwarding per Namespace in dynamic config:
 
    ```yaml
    system.enableNamespaceNotActiveAutoForwarding: