desktop: prebuilt pacman package + verified .deb (tasks 2022, 2074)

Native packages the installer can actually fetch, before task 2014 wires up
the fetching.

Arch (task 2022, re-scoped): the source PKGBUILD is gone — asking every user
to install rust+node and compile for minutes isn't distribution. Replaced by
desktop/packaging/arch/package-prebuilt.sh, which wraps the binary the Linux
job already built into a .pkg.tar.zst. No second Rust build, no Arch CI image:
the binary bundles nothing and resolves webkit/gtk/soup by soname, identical
on both distros, with SQLite compiled in and glibc used in the safe
built-old/run-new direction. CI is Debian and has no pacman, so the step logs
.PKGINFO plus the full file listing for audit instead of pretending to verify.

Debian (task 2074): install.sh hands the .deb to every Debian/Ubuntu user and
nothing had ever inspected it. tauri.conf.json now declares
libwebkit2gtk-4.1-0 + libgtk-3-0 explicitly rather than trusting inference —
and deliberately declares no appindicator or sqlite dep, since tauri is built
with features=[] and rusqlite is "bundled". desktop/packaging/deb/verify.sh
prints the generated control file, cross-checks it against what the ELF
actually needs via dpkg-shlibdeps, confirms every declared dep exists in apt,
and clean-container installs when a docker CLI is available.

Both artifacts join the run artifact and the tagged release; install.sh grows
a pacman branch so Arch/CachyOS gets a native install instead of the AppImage
fallback. Still no release cut (rule 2).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

desktop/packaging/publish-release.sh

@@ -16,6 +16,7 @@
 # The build + de-bundle steps run first; this consumes their output:
 #   desktop/src-tauri/target/release/bundle/appimage/*.AppImage  (de-bundled)
 #   desktop/src-tauri/target/release/bundle/deb/*.deb
+#   desktop/src-tauri/target/release/bundle/arch/*.pkg.tar.*     (prebuilt pacman)
 #
 # Instance-agnostic: server + repo come from the runner's github.* context
 # (Forgejo populates them for compatibility), so nothing is hardcoded to one host.
@@ -42,6 +43,7 @@ shopt -s nullglob
 ASSETS=(
   "$BUNDLE_ROOT"/appimage/*.AppImage
   "$BUNDLE_ROOT"/deb/*.deb
+  "$BUNDLE_ROOT"/arch/*.pkg.tar.*
 )
 if [ ${#ASSETS[@]} -eq 0 ]; then
   echo "ERROR: no bundles under $BUNDLE_ROOT — did the tauri build run?" >&2
@@ -74,7 +76,7 @@ first_id() { grep -oE '"id"[[:space:]]*:[[:space:]]*[0-9]+' | head -1 | grep -oE
 echo "==> Creating release for $TAG"
 BODY=$(cat <<JSON
 {"tag_name":"$TAG","name":"ThoughtSync $TAG","draft":false,"prerelease":false,
- "body":"ThoughtSync desktop $TAG. Linux AppImage (de-bundled graphics — renders on any GPU/Wayland setup) + .deb.\n\nInstall / update:\n\`\`\`\ncurl -fsSL $GITHUB_SERVER_URL/$GITHUB_REPOSITORY/raw/branch/main/desktop/packaging/install.sh | sh\n\`\`\`"}
+ "body":"ThoughtSync desktop $TAG.\n\n- **Debian / Ubuntu** — native \`.deb\`\n- **Arch / CachyOS** — native \`.pkg.tar.zst\`\n- **everything else** — \`.AppImage\` (de-bundled graphics: renders on any GPU/Wayland setup)\n\nInstall / update — picks the right one for your system:\n\`\`\`\ncurl -fsSL $GITHUB_SERVER_URL/$GITHUB_REPOSITORY/raw/branch/main/desktop/packaging/install.sh | sh\n\`\`\`"}
 JSON
 )
 # 409 = a release for this tag already exists (re-run) — fall through to lookup.