Fix Flatpak updates and bump to 0.21.1 (#7020)

* fix(flatpak): allow release checks and self-update helpers

* test: keep Flatpak permission parsing within strict Clippy rules

* chore: bump version to 0.21.1 for the Flatpak update fix

packaging/linux/flatpak/ai.storyteller.pdfcraft.bundle.yml

@@ -17,6 +17,8 @@ runtime-version: '25.08'
 sdk: org.freedesktop.Sdk
 command: pdfcraft
 finish-args:
+  # The shared updater inspects and updates this installation via flatpak-spawn --host.
+  - --talk-name=org.freedesktop.Flatpak
   - --filesystem=xdg-data/ArtCraft/versions:ro
   # Display: Wayland first; X11 only when no Wayland compositor is running.
   - --socket=wayland

packaging/linux/flatpak/ai.storyteller.pdfcraft.yml

@@ -18,6 +18,8 @@ sdk-extensions:
   - org.freedesktop.Sdk.Extension.rust-stable
 command: pdfcraft
 finish-args:
+  # The shared updater inspects and updates this installation via flatpak-spawn --host.
+  - --talk-name=org.freedesktop.Flatpak
   - --filesystem=xdg-data/ArtCraft/versions:ro
   # Display: Wayland first; X11 only when no Wayland compositor is running.
   - --socket=wayland