Two code-review findings:
1. Add a guard in cmake/install_desktop_entry.cmake that fails visibly when both
XDG_DATA_HOME and HOME are unset or empty, preventing silent installation to
the filesystem root in minimal CI sandboxes.
2. Replace the plan's tail-based verification with grep, because cmake's
FATAL_ERROR message and ninja's "build stopped" lines push the actual
rejection message out of the last four lines. The grep command reliably finds
the expected "desktop-file-validate rejected" string.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Five tasks, each ending in a commit: the two SVGs with build-time xmllint
validation, the window icon plus the registration move and the app icons:
assertion, the AdwAboutDialog migration, the opt-in desktop-entry target, and
the documentation with the full regression run.
Written assertion-first, since the project has no unit suite: each task's first
step adds the probe or dump line and watches it read MISSING. Both negative
tests are real -- one breaks an SVG comment and requires the build to fail, the
other breaks Type= and requires the target to FATAL_ERROR.
