fix(frontend): InviteUserDialog uses hardcoded mock users

[mrveiss]

Problem

InviteUserDialog invitation feature only works with 5 hardcoded test accounts, blocking real user collaboration.

Root Cause

Line 39 in InviteUserDialog.vue uses hardcoded mock users instead of fetching from backend API:

const mockUsers = [
  { id: 'user-1', username: 'alice', ... },
  { id: 'user-2', username: 'bob', ... },
  // ... 3 more hardcoded users
]

Impact

• Users cannot invite real team members
• Collaboration features blocked for production use
• Related to Issue [Frontend] Collaborative Session UI (#608 Phase 6) #874 (Collaborative Session UI Phase 6)

Files

• autobot-frontend/src/components/collaboration/InviteUserDialog.vue

Solution

Replace mockUsers with API call to /api/users or equivalent endpoint