feat: add participant interview link action

Add a copy button to scheduled interview sessions with confirmation, clipboard error handling, and regression coverage.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/app/App.test.tsx

@@ -814,6 +814,7 @@ describe('Go Guess frontend', () => {
   it('edits shared documentation and displays notes received over authenticated fetch streaming', async () => {
     authenticate()
     const user = userEvent.setup()
+    const writeText = vi.spyOn(navigator.clipboard, 'writeText')
     const scheduled = {
       id: 80,
       jobId: 7,
@@ -866,6 +867,11 @@ describe('Go Guess frontend', () => {
     })
     renderApp('/scheduled-interviews/80')
     expect(await screen.findByText('Strong system design answer.')).toBeInTheDocument()
+    await user.click(screen.getByRole('button', { name: 'Copy participant interview link' }))
+    expect(writeText).toHaveBeenCalledWith('/participant/meeting/meeting-token')
+    expect(
+      screen.getByRole('button', { name: 'Copy participant interview link' }),
+    ).toHaveTextContent('Link copied')
     const document = screen.getByLabelText('Shared documentation')
     await user.clear(document)
     await user.type(document, 'Updated candidate exercise')

frontend/src/features/interviews/pages.tsx

@@ -1,4 +1,4 @@
-import { Check, UsersRound, X } from 'lucide-react'
+import { Check, Copy, UsersRound, X } from 'lucide-react'
 import { type FormEvent, useEffect, useMemo, useState } from 'react'
 import { Link, useParams } from 'react-router-dom'
 import { api, ApiError } from '../../api/client'
@@ -145,6 +145,7 @@ export function ScheduledInterviewPage() {
   const [notes, setNotes] = useState<ScheduledInterview['notes']>([])
   const [error, setError] = useState('')
   const [saving, setSaving] = useState(false)
+  const [linkCopied, setLinkCopied] = useState(false)
 
   useEffect(() => {
     let active = true
@@ -218,6 +219,16 @@ export function ScheduledInterviewPage() {
     }
   }
 
+  async function copyParticipantLink(url: string) {
+    setError('')
+    try {
+      await navigator.clipboard.writeText(url)
+      setLinkCopied(true)
+    } catch {
+      setError('Could not copy the participant interview link')
+    }
+  }
+
   if (!interview && !error) return <Loading />
   if (!interview) return <ErrorAlert error={error} />
   return (
@@ -236,6 +247,15 @@ export function ScheduledInterviewPage() {
       {error && <ErrorAlert error={error} />}
       <DateAndPlace interview={interview} />
       <div className="session-actions">
+        <button
+          className="button secondary"
+          type="button"
+          onClick={() => void copyParticipantLink(interview.candidateUrl)}
+          aria-label="Copy participant interview link"
+        >
+          {linkCopied ? <Check size={17} /> : <Copy size={17} />}
+          {linkCopied ? 'Link copied' : 'Copy participant link'}
+        </button>
         {interview.status !== 'started' && interview.status !== 'completed' && (
           <button
             className="button primary"