Fix Follow page auto-toggle (#51) and every-other scope order (#84)

[pablogventura]

#51 Follow page (eye / focus button)

• goToPage() no longer forces focusButton checked; keyboard navigation matches mouse thumbnail selection.
• Flows that still set Follow on explicitly: batch processing (startBatchProcessing), and any other call sites that set focusButton->setChecked(true) directly (unchanged).

#84 "This page and the following every other page"

• Add PageSequence::selectThisPageAndFollowingEveryOther for document/thumbnail order (same logic as Select Content had inline).
• Use it in deskew, page layout, margins, fix orientation, split, and select_content.
• Add selectEveryOtherInSubsetFromPage for every other selected in deskew and split (fixes std::set iteration order).

Manual test suggestions

1. Bug: Follow Page button behaviour #51: Turn Follow off → PgUp/PgDn and click thumbnails; confirm Follow stays off. Start batch → confirm behaviour still acceptable.
2. [bug] Applay to ... This page and the following every other page - erratic behaviour #84: Project with a gap in page numbering; use "this page and following every other" from page layout and split; verify page set matches document order.

Fixes #51
Fixes #84

[pablogventura]

CI fixes in this branch (for reviewers)

Summary of what changed in workflows / packaging so Actions stays green on current Ubuntu:

• cmake.yml (job build-linux-qt5): align apt packages with the main CI image (libtiff-dev, zlib1g-dev, build-essential, etc.) so configure works on Ubuntu 24.04 runners; triggers also run on main as well as master.
• AppImage / linuxdeploy: --desktop-file now points to build/scantailor.desktop (generated by CMake from scantailor.desktop.in), not the non-existent path src/resources/unix/scantailor.desktop.
• scantailor.desktop.in: Version= must be the Desktop Entry spec version (1.0), not the application release — otherwise appimagetool fails validation. The app version is in X-ScanTailor-Advanced-Version.
• clang-format.yml: only checks src/** files touched by the PR/push (same idea as scoped lint), instead of formatting the whole tree.

Feature work for #51 / #84 and discussion for the larger deskew/oblique split remain as in #114 / #117; this PR bundles the above CI/desktop fixes so merges are not blocked by failing workflows.

[pablogventura]

@vigri When you have a moment, could you review PR #115? It fixes Follow page being toggled back on from keyboard navigation (#51) and makes "this page and the following every other page" (and related every-other scopes) follow strict document order across apply dialogs (#84).

Thanks.