feat(cli): promote tasks commands from experimental to GA (#20916)

## Overview

This change promotes the tasks CLI commands from `coder exp task` to
`coder task`, marking them as generally available (GA).

## Migration

Users will need to update their scripts from:

```shell
coder exp task create "my task"
```

To:
```shell
coder task create "my task"
```

---

🤖 This change was written by Claude Sonnet 4.5 Thinking using [mux](https://github.com/coder/mux) and reviewed by a human 🏄🏻‍♂️

cli/task_send.go

@@ -0,0 +1,77 @@
+package cli
+
+import (
+	"io"
+
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/codersdk"
+	"github.com/coder/serpent"
+)
+
+func (r *RootCmd) taskSend() *serpent.Command {
+	var stdin bool
+
+	cmd := &serpent.Command{
+		Use:   "send <task> [<input> | --stdin]",
+		Short: "Send input to a task",
+		Long: FormatExamples(Example{
+			Description: "Send direct input to a task.",
+			Command:     "coder task send task1 \"Please also add unit tests\"",
+		}, Example{
+			Description: "Send input from stdin to a task.",
+			Command:     "echo \"Please also add unit tests\" | coder task send task1 --stdin",
+		}),
+		Middleware: serpent.RequireRangeArgs(1, 2),
+		Options: serpent.OptionSet{
+			{
+				Name:        "stdin",
+				Flag:        "stdin",
+				Description: "Reads the input from stdin.",
+				Value:       serpent.BoolOf(&stdin),
+			},
+		},
+		Handler: func(inv *serpent.Invocation) error {
+			client, err := r.InitClient(inv)
+			if err != nil {
+				return err
+			}
+
+			var (
+				ctx        = inv.Context()
+				exp        = codersdk.NewExperimentalClient(client)
+				identifier = inv.Args[0]
+
+				taskInput string
+			)
+
+			if stdin {
+				bytes, err := io.ReadAll(inv.Stdin)
+				if err != nil {
+					return xerrors.Errorf("reading stdio: %w", err)
+				}
+
+				taskInput = string(bytes)
+			} else {
+				if len(inv.Args) != 2 {
+					return xerrors.Errorf("expected an input for the task")
+				}
+
+				taskInput = inv.Args[1]
+			}
+
+			task, err := exp.TaskByIdentifier(ctx, identifier)
+			if err != nil {
+				return xerrors.Errorf("resolve task: %w", err)
+			}
+
+			if err = exp.TaskSend(ctx, codersdk.Me, task.ID, codersdk.TaskSendRequest{Input: taskInput}); err != nil {
+				return xerrors.Errorf("send input to task: %w", err)
+			}
+
+			return nil
+		},
+	}
+
+	return cmd
+}