Add openFile hook to AttachesTool to support custom file opening logic

[pasichDev]

This update introduces a new openFile hook to the AttachesTool config.
It allows custom file-opening logic beyond the default browser behavior.

This is especially useful for:

• WebView environments (Android/iOS apps)
• Desktop applications that embed Editor.js
• Custom file viewers / sandboxed environments

When the hook is present, openFile(fileData) is executed instead of opening file.url in a new tab.
If the hook is missing or throws an error — the fallback browser action is triggered.

📌 Why this is useful
✔ Works in Android WebView

Browser links (target=_blank) do not work in WebView — but you can call the Android method.

🧩 Short PR Example Description
Added a new config option openFile to AttachesTool.
If provided, it overrides the default action when the user clicks the file icon.
Useful for WebView apps (Android/iOS), desktop clients, and custom environments where
opening external URLs is restricted. Falls back to the standard browser behavior
when not defined.

[pasichDev]

Added a proper fallback for attachment title rendering.

If data.title is empty or missing, the UI now automatically uses file.name as the visible title.

This fixes the issue where freshly uploaded attachments appeared in the editor without a human-readable name.

Why

Previously, after uploading a file, the title field was often empty, resulting in a blank placeholder in the attachments block.
The user expected to see the original file name by default.

How it works

In showFileData():

this.nodes.title.textContent = title || file.name || '';

Now:
title — used if user typed or previously saved it
file.name — used automatically when no title provided

'' — fallback to avoid undefined/null

Result
Attachments now display correct filenames immediately after upload, improving clarity and UX.

[pasichDev]

Hi @neSpecc!
I’ve opened a PR — could you please take a look when you have a moment?
Thanks!
#83