Linux app id: ai.storyteller.solidcraft, with an end-of-life rebase from the old id (#619)

The Flatpak app id, desktop/metainfo/MIME file names, icon name and the window's Wayland app_id / X11 class are now ai.storyteller.solidcraft, the id the ArtCraft launcher expects.

Existing Flatpak installs move over: the Pages repo marks app/ai.storyteller.solvecraft end-of-life with a rebase to the new id, so flatpak update offers the switch and Flatpak carries ~/.var/app along. A new install next to the old one copies settings and autosaves on first launch through a read-only grant on the old data folder. The metainfo declares <replaces>/<provides>, the desktop entry X-Flatpak-RenamedFrom, and AppImages drop the menu entry an older AppImage installed. deb/rpm upgrades remove the old-named files.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/releasing.md

@@ -11,7 +11,7 @@ version bump and no patch release for every merge.
 Every release asset, binary, installer product name and package uses the SolidCraft name
 (`solidcraft-<version>-linux-<arch>.AppImage`, `SolidCraft-<version>-windows-x64.exe`,
 `solidcraft-cli` archives, …). The old name survives only in the shims listed in
-[compatibility.md](compatibility.md) (the Linux app ID, the legacy `.zsync` and `.flatpakrepo`
+[compatibility.md](compatibility.md) (the end-of-life Flatpak refs of the old Linux app ID, the legacy `.zsync` and `.flatpakrepo`
 copies, the deprecated old-name CLI alias); keep them until that document says they can go. Do not
 rewrite published assets, checksums, tags or historical release notes of earlier versions.