improve OCR quality, perspective correction, and translations

Sharpen perspective warps by switching to Lanczos4 interpolation and
tighten the aspect-ratio tolerance so photos are no longer wrongly
stretched to Letter/A4.  Gentle margin corrections now go through a
validation step with a Laplacian detail-loss check, preventing false
positives on born-digital pages.

Skip the scanner effect on pages that already have a clean white
background (born-digital PDFs), which was hurting OCR accuracy on
those documents.

Run the PDF editor as a separate D-Bus instance so it no longer
conflicts with an open OCR window.

Bump the font-size scale factor to 0.90 for better text positioning
in searchable PDFs.  Fix the small-image skip logic so wide/thin
images (terminals, banners) are no longer discarded.

Update translations in 22 locales — the Dewarp label and several
other UI strings were still showing in English.

Author: bigbruno