docs: fix the streamable client snippet to use (*Client).Connect (#1142)

### What was broken

`docs/protocol.md` → *Streamable Transport* → client side shows:

```go
client, err := mcp.Connect(ctx, transport, &mcp.ClientOptions{...})
```

There is no top-level `mcp.Connect`. The package has
`(*Client).Connect`, whose
third parameter is `*ClientSessionOptions`, not `*ClientOptions`. So the
one
snippet a reader reaches for when wiring up the client side of
streamable HTTP
does not build.

It is also the only outlier in the docs: `quick_start.md`, `client.md`,
`server.md`, `troubleshooting.md` and `protocol.md` itself (lines 470,
538) all
already use `client.Connect(ctx, transport, nil)`.

### How I checked

Pasted the snippet verbatim into a fresh module requiring the released
SDK
(`github.com/modelcontextprotocol/go-sdk v1.7.0`):

```
$ go build ./...
./broken.go:15:21: undefined: mcp.Connect
```

Then ran the proposed replacement end to end against a real streamable
server
(`mcp.NewStreamableHTTPHandler` behind `httptest.NewServer`), connecting
and
calling a tool over the session:

```
BUILD OK
tool result: {"greeting":"Hi you"}
```

### What it is now

```go
transport := &mcp.StreamableClientTransport{
	Endpoint: "http://localhost:8080/mcp",
}
client := mcp.NewClient(&mcp.Implementation{Name: "client", Version: "v1.0.0"}, nil)
session, err := client.Connect(ctx, transport, nil)
```

Change is in `internal/docs/protocol.src.md`; `docs/protocol.md`
regenerated with
`go generate ./internal/docs`, both committed together. Docs-only, no
code paths
touched.

---
Assisted-by: Claude Opus 5 — this PR was drafted and verified by Anton's
AI
cofounder running on his account; the commands and outputs above are
from real
runs, not reconstructions.

Co-authored-by: Anton Dzyatkovsky <dzyatkovskiy.a@gmail.com>

docs/protocol.md

@@ -256,7 +256,8 @@ connect to the server:
 transport := &mcp.StreamableClientTransport{
 	Endpoint: "http://localhost:8080/mcp",
 }
-client, err := mcp.Connect(ctx, transport, &mcp.ClientOptions{...})
+client := mcp.NewClient(&mcp.Implementation{Name: "client", Version: "v1.0.0"}, nil)
+session, err := client.Connect(ctx, transport, nil)
 ```
 
 The `StreamableClientTransport` handles the HTTP requests and communicates with