Do not start GRPC server unless specified

[mkysel]

Gate gRPC server startup behind options.API.Enable and add a deprecation bridge for --replication.enable in cmd/replication/main.go

• Switch all server and validation gating from options.Replication.Enable to options.API.Enable, including conditional DB init and API startup in cmd/replication/main.go, pkg/config/validation.go, and pkg/server/server.go.
• Create the gRPC listener only when --api.enable is true; require a non-nil listener only when starting the API in pkg/server/server.go.
• Add a deprecation bridge in cmd/replication/main.go: when --replication.enable is set without --api.enable, log a warning and set options.API.Enable=true.
• Introduce Enable and SendKeepAliveInterval on config.APIOptions, deprecate config.ReplicationOptions to Enable only, and add -p short flag for port in pkg/config/options.go.
• Update services and tests to use config.APIOptions and API: true, including pkg/api/message/service.go, pkg/testutils/server/server.go, and multiple tests.
• Replace XMTPD_REPLICATION_ENABLE with XMTPD_API_ENABLE in dev scripts and test utils in dev/run, dev/run-2, and pkg/integration/docker_utils_test.go.

📍Where to Start

Start in the main function of cmd/replication/main.go to see option consolidation, deprecation handling, and the new API gating, then follow into server.NewReplicationServer in pkg/server/server.go.

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Macroscope summarized 7d7a28f.

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