Paste insertion overwrites clipboard without restoring

[poodle64]

Description

When text output method is set to paste (the fast method), the transcribed text is placed on the clipboard and pasted via Cmd+V. The original clipboard content is not reliably preserved and restored after insertion.

Users lose whatever was on their clipboard before the transcription completed.

Expected Behaviour

1. Save current clipboard contents before paste insertion
2. Place transcribed text on clipboard
3. Simulate Cmd+V paste
4. Wait for paste to complete
5. Restore original clipboard contents

Current Behaviour

Clipboard content is overwritten by the transcribed text and not restored (or restoration is unreliable).

Acceptance Criteria

• Original clipboard content preserved across paste insertion
• Configurable restore delay to account for slow applications
• Works with both plain text and rich text clipboard content
• Graceful fallback if clipboard cannot be read (e.g. image content)

References

• src-tauri/src/text_insert.rs (insertion logic)
• src-tauri/src/clipboard.rs (clipboard operations)
• Feature docs: docs/product/features/text-output/F05-design-principles.md