designer overhaul, drag-drop reordering, and page-size/scripting fixes

- Batch-aware scanning/importing: split-button "scan/import to current
  batch or document" alternatives, a shared continue-scanning prompt, and
  batch divider rows in the Inbox (click to select the whole batch)
- Trash: Empty Trash action, now documented in Help for the first time
- Capture Profile designer: three-section navigation (Capture Profile /
  Document Types / Test Capture), an Overview hint when no document types
  exist yet, document-type Remove now confirms first, and drag-handle
  reordering for document types and index fields (replacing Up/Down)
- Page thumbnail strip: drag-drop now shows an insertion-line indicator
  and supports moving a page to the very last position
- Capture profile picker: a "None" entry always listed first, replacing
  the separate clear button
- Fixed oversized PDF pages from scanned/imported documents (DPI was
  being passed to the PDF writer as points)
- Fixed a crash materializing a single-page scan or non-PDF import
- Removed Therefore export's Fixed/Constant value mapping option and
  fixed a bug where adding a field wiped existing Therefore mappings
- Hidden index fields now group at the bottom of the field list
- Updated in-app Help throughout, with more scripting detail

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013rQiSGeAgS1fAWtvh3s2vm