Pixee 0.4.0

Linux packaging. Pixee can now be built and installed as a Flatpak, which
brings with it the desktop integration it never had on Linux: an app icon, a
launcher entry, and metadata for software centres.

This is a quiet release if you're on Windows — the only thing you'll notice is
that the window finally has an icon. The full feature and keyboard list lives in
README.

Flatpak

flatpak install flathub org.kde.Platform//6.11 org.kde.Sdk//6.11 org.flatpak.Builder
flatpak run org.flatpak.Builder --user --install --force-clean \
    build packaging/net.dynart.Pixee.yml
flatpak run net.dynart.Pixee

The manifest builds from the working tree, so you don't need a tag or even a
commit to try one.

Pixee is not on Flathub yet. The packaging is done and verified, but
publishing needs a few things that aren't code — see
docs/flathub-requirements.md.

It reads more formats than the native build

The Flatpak runs on the KDE runtime, which bundles kimageformats. So it opens
HEIC/HEIF, AVIF, JPEG XL, PSD/PSB, XCF, KRA, ORA, DDS, QOI and SVG with no
extra work — the plugin juggling the Windows build needs
(docs/windows-extra-image-formats.md) has no
equivalent here. It's the single biggest practical difference between the two.

What the sandbox changes

A Flatpak runs confined, and three things follow from that:

• Pixee asks for full filesystem access, because it's a file manager for
  images — it browses your folders with its own tree and moves files between
  them. The alternative sandbox mechanism hands over one file at a time, which
  can't express that.
• It keeps its own data under ~/.var/app/net.dynart.Pixee/, separate from
  a native install's.
• "Open with" uses your desktop's application chooser instead of Pixee's own
  configurable program list. Inside a sandbox the programs on that list aren't
  reachable, so the desktop has to make the handoff.

The Linux data folder moved

Pixee's thumbnail cache and user themes now live in the standard location —
~/.local/share/Dynart/Pixee instead of ~/.pixee.

You don't have to do anything: your existing cache is carried across the first
time you run 0.4.0, so you keep the thumbnails you already have, and a user
theme left in ~/.pixee/themes/ still works.

Windows is unchanged — it keeps ~/.pixee, where existing installs already
look.

The reason for the split is the Flatpak. It's granted access to your real home
so it can browse it, which means a path built from "your home folder" would
write into your actual home rather than the app's own storage. The standard
location resolves correctly in both cases.

Installing from source on Linux

make install now follows the normal freedesktop layout under a configurable
prefix, so a build lands where a Linux system expects it — binary in bin/,
themes in share/pixee/, and the icon, launcher entry and metadata in their
usual places:

qmake PREFIX=/usr/local Pixee.pro
make
sudo make install

Previously the only install rule put the binary in /opt/Pixee/bin and left the
themes behind entirely.

For contributors

• docs/flatpak.md — the technical reference: what the sandbox
  changes about the app, which permissions it asks for and why, which linter
  errors are expected, and how to cut a release Flathub can build.
• docs/flathub-requirements.md — the submission
  checklist.