Add preview card with modal for pasted long content in PromptInput

Currently, when pasting long text into PromptInput, the entire content is displayed inline, which can make the input area unwieldy.

Expected behavior:
Long pasted content should be displayed as a compact preview card (similar to Claude.ai and v0.app), showing:

• A truncated preview of the content
• File size and line count
• A "PASTED" badge/indicator
• Clicking the card opens a modal/dialog with the full content
• Modal should include actions to copy or download the pasted content

Current behavior:
All pasted text appears directly in the textarea, regardless of length.

Screenshots:

Suggested implementation:
Add a PromptInputPastedContent component that detects large pastes (e.g., >200 characters or >10 lines) and displays them as a clickable preview card above the textarea. The card should trigger a modal/dialog showing the full content with copy and download actions.

Start at the existing PromptInput implementation and inspect how pasted text is handled. Add the proposed PromptInputPastedContent entry point for large pastes, with a truncated card showing size, line count, and a PASTED indicator, then verify that opening it reveals the full content with copy and download actions.