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/src-tauri/tauri.conf.json

@@ -38,6 +38,11 @@
       "icons/128x128.png",
       "icons/128x128@2x.png",
       "icons/icon.png"
-    ]
+    ],
+    "linux": {
+      "deb": {
+        "depends": ["libwebkit2gtk-4.1-0", "libgtk-3-0"]
+      }
+    }
   }
 }