Refresh playground docs for threads and files

docs/toolhive/guides-ui/playground.mdx

@@ -36,6 +36,16 @@ MCP servers directly through natural language commands. You can list servers,
 check their status, start or stop them, and perform other management tasks using
 conversational AI.
 
+### Threaded conversations
+
+Keep multiple chats organized in a sidebar with starred and recent groups. See
+[Manage playground threads](#manage-playground-threads).
+
+### Attachments
+
+Send images and PDFs alongside your prompt. See
+[Attach files to a message](#attach-files-to-a-message).
+
 ## Getting started
 
 To start using the playground:
@@ -93,6 +103,14 @@ To start using the playground:
    have access to all enabled MCP tools and can execute them based on your
    requests.
 
+5. **Manage chat threads**: See
+   [Manage playground threads](#manage-playground-threads) for sidebar, rename,
+   star, and delete actions.
+
+6. **Attach images or PDFs**: See
+   [Attach files to a message](#attach-files-to-a-message) for supported types
+   and limits.
+
 ## Using the playground
 
 ### Testing MCP server functionality
@@ -173,6 +191,89 @@ The playground shows detailed information about each tool execution:
 This visibility helps you understand exactly how your MCP servers are behaving
 and identify any issues with tool implementation or configuration.
 
+### Manage playground threads
+
+The playground keeps each conversation in a separate thread so you can run
+several testing sessions in parallel without losing context. Open the sidebar to
+see your threads, with **Starred** entries pinned at the top and **Recents**
+below. Untitled threads show as `New chat` until you give them a name.
+
+Each row shows a relative timestamp such as `just now`, `5m ago`, `2h ago`, or
+`3d ago`. Older threads show a short date instead.
+
+To work with threads:
+
+- **Start a new thread**: Click **New chat** at the top of the sidebar.
+- **Rename a thread**: Double-click the thread row, or open its **Thread
+  options** menu and choose **Rename**. You can also click the title or the
+  pencil icon at the top of the chat to rename the active thread. The thread
+  row's tooltip confirms the double-click action:
+
+  > Double-click to rename
+
+- **Star or unstar a thread**: Click the star icon next to the thread title, or
+  open **Thread options** and choose **Star** or **Unstar**. Starred threads
+  appear under **Starred** at the top of the sidebar.
+- **Delete or unstar threads**: Open **Thread options** and choose **Delete** to
+  remove a thread you no longer need. The playground asks for confirmation:
+
+  > Delete "`<THREAD_NAME>`"? This cannot be undone.
+
+  Confirm with **Delete**, or back out with **Cancel**.
+
+### Attach files to a message
+
+Add images and PDFs to a message so the model can read them while it works with
+your MCP tools. The composer accepts up to 5 files per message, each 10 MB or
+smaller, and supports image files and PDFs.
+
+To attach files:
+
+1. Open the composer toolbar menu and choose **Add images or PDFs**, or drag
+   files onto the playground window. Drag-and-drop is enabled across the entire
+   playground.
+2. Type your prompt and send the message. If you send a message that only
+   contains attachments, the playground records the message text as:
+
+   > Sent with attachments
+
+In the chat history, the playground previews each attachment alongside the
+message:
+
+- **Images** appear inline. Click an image to open it in a larger modal preview.
+- **PDFs** show as `📎 <FILE_NAME>` with a **Download** link so you can save the
+  original file.
+
+If a file is rejected, the playground shows a toast that explains why:
+
+- When you exceed the per-message limit:
+
+  > You reached the maximum number of files
+  >
+  > You can only upload up to 5 files
+
+- When a file is over 10 MB:
+
+  > File size too large
+  >
+  > The file size must be less than 10MB
+
+- When a file isn't an image or a PDF:
+
+  > File type not supported
+  >
+  > Only images and PDFs are supported
+
+The composer placeholder reflects the playground state:
+
+> Select an AI model to get started
+
+is shown when no model is selected, then:
+
+> Type your message...
+
+once you've chosen one.
+
 ## Recommended practices
 
 ### Provider security
@@ -201,6 +302,16 @@ and identify any issues with tool implementation or configuration.
 4. **Error handling**: Intentionally trigger error conditions to validate proper
    error handling
 
+### Thread and attachment hygiene
+
+- Delete unused threads so the sidebar stays focused on the work you actually
+  return to.
+- Star the conversations you want to keep close at hand. Otherwise they get
+  pushed down as new chats arrive in **Recents**.
+- Attachments are sent to your AI provider. Strip credentials, customer
+  information, and other sensitive content from PDFs and screenshots before
+  sharing them.
+
 ## Next steps
 
 - Learn about [client configuration](./client-configuration.mdx) to connect