Platform Issue: Add one-click copy for Connector Builder stream-test failures

## Platform Version

Not specified — this is a feature request based on the Connector Builder stream-test UI.

## What step the error happened?

Other — Connector Builder stream test.

## Relevant information

### Problem

When a Connector Builder stream test fails, users often need to share the error with a teammate or attach it to a support request.

The current test panel requires users to drag-select the visible error text manually, then repeat that for the internal message or stacktrace after expanding the details. This is slow and error-prone for long logs: important lines can be missed or copied incompletely.

### Proposal

Add a `Copy` action to each error card in the Connector Builder stream-test panel. Place it in the existing right-side action area, immediately left of the details toggle, so it is available without adding a separate control row.

The action should copy the available user-facing error message, internal message, and stacktrace as one clipboard value, with one item per line.

### Expected outcome

Users can copy a complete failure report with one click and paste it into a support ticket, chat, or issue without manually selecting the text.

### Prototype

A local Storybook prototype was verified with the current and proposed states, including the clipboard action.

## Relevant log output

No runtime logs. This is a UX improvement request for how failed stream-test logs are copied.

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**Internal Tracking:** https://github.com/airbytehq/oncall/issues/13158

Start by locating the Connector Builder stream-test panel and its error cards, then inspect the existing right-side action area and the Storybook prototype referenced in the issue. Done means each error card has a Copy action that places the user-facing message, internal message, and stacktrace into the clipboard, one item per line.

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