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/testdata/coder_task_delete_--help.golden

@@ -0,0 +1,27 @@
+coder v0.0.0-devel
+
+USAGE:
+  coder task delete [flags] <task> [<task> ...]
+
+  Delete tasks
+
+  Aliases: rm
+
+    - Delete a single task.:
+  
+       $ $ coder task delete task1
+  
+    - Delete multiple tasks.:
+  
+       $ $ coder task delete task1 task2 task3
+  
+    - Delete a task without confirmation.:
+  
+       $ $ coder task delete task4 --yes
+
+OPTIONS:
+  -y, --yes bool
+          Bypass prompts.
+
+———
+Run `coder --help` for a list of global options.