docs(connect): add client documentation and operations mode

[asoorm]

Rendered Mermaids:

sequenceDiagram
    autonumber
    participant Provider as API Provider
    participant CLI as Cosmo CLI (wgc)
    participant Consumer as API Consumer
    participant Client as Client SDK
    participant Router as Cosmo Router
    participant Graph as Federated Graph
    Note over Provider, Router: Setup & Configuration
    Provider->>Provider: Define GraphQL Operations (.graphql)
    Provider->>CLI: Generate Protobuf (wgc grpc-service generate)
    CLI->>Provider: service.proto + lock file
    Provider->>Router: Configure & Start Router with operations
    
    Note over Provider, Consumer: Distribution
    Provider->>Consumer: Distribute service.proto / OpenAPI spec
    Note over Consumer, Client: Client Development
    Consumer->>Consumer: Generate Client SDK (buf/protoc)
    Consumer->>Client: Integrate SDK into App
    Note over Client, Graph: Runtime
    Client->>Router: Send RPC Request (Connect/gRPC)
    Router->>Graph: Execute GraphQL Operation
    Graph-->>Router: GraphQL Response
    Router-->>Client: Protobuf Response
    Note over Provider, Router: Observe
    Router->>Provider: OTEL Metrics / Traces (GraphQL & RPC)

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