feat: promote Tasks to GA (#20923)

## Summary

This change promotes Coder Tasks from Beta to GA by removing Beta labels
from:

- TasksPage UI component
- Documentation files

Tasks feature is now ready for general availability!

---

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

docs/ai-coder/index.md

@@ -8,11 +8,11 @@ Coder [integrates with IDEs](../user-guides/workspace-access/index.md) such as C
 
 These agents work well inside existing Coder workspaces as they can simply be enabled via an extension or are built-into the editor.
 
-## Agents with Coder Tasks (Beta)
+## Agents with Coder Tasks
 
 In cases where the IDE is secondary, such as prototyping or long-running background jobs, agents like Claude Code or Aider are better for the job and new SaaS interfaces like [Devin](https://devin.ai) and [ChatGPT Codex](https://openai.com/index/introducing-codex/) are emerging.
 
-[Coder Tasks](./tasks.md) is a new interface inside Coder to run and manage coding agents with a chat-based UI. Unlike SaaS-based products, Coder Tasks is self-hosted (included in your Coder deployment) and allows you to run any terminal-based agent such as Claude Code or Codex's Open Source CLI.
+[Coder Tasks](./tasks.md) is an interface inside Coder to run and manage coding agents with a chat-based UI. Unlike SaaS-based products, Coder Tasks is self-hosted (included in your Coder deployment) and allows you to run any terminal-based agent such as Claude Code or Codex's Open Source CLI.
 
 ![Coder Tasks UI](../images/guides/ai-agents/tasks-ui.png)
 

docs/ai-coder/tasks.md

@@ -1,4 +1,4 @@
-# Coder Tasks (Beta)
+# Coder Tasks
 
 Coder Tasks is an interface for running & managing coding agents such as Claude Code and Aider, powered by Coder workspaces.