fix(release): latest.json entry per installer type — .deb booths could never self-update

tauri-plugin-updater resolves the download target as {os}-{arch}-{installer}
first (linux-x86_64-deb — the bundler stamps the installer type into the
binary, verified with `strings` on a local .deb) and only then bare
linux-x86_64. Our manifest carried only the bare key, pointing at the
AppImage. A .deb install therefore downloaded the AppImage, verified its
signature, then failed install_deb()'s is_deb check with
InvalidUpdaterFormat — after the download, before any relaunch. This, not
version drift or swallowed errors, is why v0.1.0→v0.1.6 never self-updated.

latest.json now carries linux-x86_64-deb, linux-x86_64-rpm (when built) and
linux-x86_64 (AppImage), each with its own .sig. A .deb update ends in a
polkit password prompt (pkexec dpkg -i) — the intended admin gate on a
root-installed package. README + wiki updated; wiki also records the v0.1.6
LIVE field verification.

Claude-Session: https://claude.ai/code/session_01FWncR69HgGPuei1dLrW3cU

apps/desktop/README.md

@@ -44,6 +44,14 @@ see that workflow's header and `wiki/decisions/desktop-shell-tauri.md`). The upd
 signing pubkey live in `tauri.conf.json`; the private signing key is held outside the repo, never
 committed.
 
+**The manifest carries one entry per installer type** (`linux-x86_64-deb`, `linux-x86_64-rpm`,
+and bare `linux-x86_64` for AppImage). The updater picks the entry matching how the running app
+was installed — a `.deb` install will only ever accept a signed `.deb`. Booths run the `.deb`,
+so an in-app update ends in a **polkit password prompt** (`pkexec dpkg -i`): that is expected,
+and it is the right gate — the package lives in `/usr/bin`, root-owned, and the operator is not
+supposed to be able to replace it silently. Cancel the prompt and the app keeps running the old
+version; the failure is logged to the server's Logs viewer.
+
 ## Release gate — run the REAL bundle locally before tagging
 
 `tauri dev` loads the SPA from `http://localhost:5173`, a plain http origin. The shipped bundle