feat: add copy feedback state to conversation timeline

[prasiddhi-105]

Description

This PR addresses the conversation timeline user experience by implementing an interactive copy verification state feedback wrapper mechanism. Users now receive instant visual confirmation whenever message snippets are cloned.

Changes Implemented

🔹 Frontend (frontend/src/components/ChatWindow.jsx)

• Updated the message snippet copy action blocks to bind with the reactive internal state engine (copiedId).
• Standardized the action bar layout so both message blocks and AI response toolbars dynamically display a checkmark/confirmation badge upon execution.
• Bound a temporary fallback timeline decay threshold (1500ms) to reset the timeline icons smoothly.

🔹 Component Verification (frontend/src/components/ChatWindow.test.jsx)

• Added an isolated unit testing file using explicit jsdom configuration headers.
• Mocked required layout layout functions (scrollIntoView) and modern browser communication boundaries (navigator.clipboard).
• Asserted accurate post-click state evaluations and proper timed cleanup decay loops using clean toBeDefined() vitest matchers.

Verification Results

The test suite successfully passed all isolated checks under the current environment:

Closes #760

[vercel]

@prasiddhi-105 is attempting to deploy a commit to the Darshan's projects Team on Vercel.

A member of the Team first needs to authorize it.