Optimize admin tools for large datasets with server-side search

[Copilot]

Admin panel became unresponsive with 8000+ users as it loaded all records into the browser at once.

Backend Changes

• Limit initial queries: Cap to 1000 active + 1000 deleted records for users and projects
• Server-side search endpoints: POST /admin/users/search and POST /admin/projects/search
• Multi-field aggregation: Search across email, name, project name, owner info, and IDs using MongoDB pipelines

// Before: Load everything
const activeUsers = await User.find({}, projection).lean().exec()

// After: Limit initial load, search server-side
const activeUsers = await User.find({}, projection).limit(1000).lean().exec()

Frontend Changes

• Debounced remote search: 300ms for users, 500ms for projects with AbortController for cancellation
• Conditional "Show All": Only display when ≤200 hidden users or ≤500 hidden projects
• Search state management: searchResults overrides local data when actively searching

useEffect(() => {
  if (!searchText.length) {
    setSearchResults(null)
    return
  }
  const abortController = new AbortController()
  const timer = setTimeout(() => {
    searchUsers(searchText, abortController.signal)
      .then(data => setSearchResults(data.users))
  }, 300)
  return () => {
    clearTimeout(timer)
    abortController.abort()
  }
}, [searchText])

Additional Fixes

• Race condition in search input handling
• User selection logic to use filtered dataset
• Password security in update endpoint

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