Add multi-select with Shift/Ctrl toggles and marquee selection on the invoice
and quote PDF template editors, plus a shared transformer, group nudge with
snap-aware arrow keys, multi copy/paste/duplicate, align-to-page or
align-to-selection, horizontal/vertical distribute, and Ctrl/Cmd+G group /
Ctrl/Cmd+Shift+G ungroup.
Expose horizontal (left/center/right/justify) and vertical (top/middle/bottom)
text controls in the properties panel; export verticalAlign, group_id,
locked, and hidden in template JSON where set. Skip hidden elements in
ReportLab rendering; draw justified text on canvas via Paragraph; honor
verticalAlign when a text box height is present.
Introduce app/static/js/pdf_editor helpers (loaded with dynamic import from
the templates), pdf_editor.css, a layers panel with visibility and lock toggles,
smart-guide snapping, and optional ruler chrome. Document behaviour and manual
QA in docs/PDF_LAYOUT_EDITOR.md; add tests/test_pdf_template_schema.py for
optional template fields.
Closes#619.
Dries Peeters