Fix macOS Theseus build issue, cleanup platform specific code (#3604)

* chore(theseus): significantly cleanup MacOS-specific code

* fix(labrinth): only use jemalloc allocator for Linux targets

The upstream crate asserts that its tests only pass for Linux targets,
and there's little point in supporting other OS for now since practical
Labrinth deployments run under a Linux environment anyway. This change
made it easier for me to cross-compile Labrinth.

* chore(theseus): tweak traffic lights pos according to c39bb78e38

As far as I understand it, that PR introduced the seemingly ad-hoc
additions of 6 and 12 units to the traffic light position calculations,
not directly modifying the `const` values introduced by
d6a72fbfc4.

* fix: re-enable app window shadows on Linux

* chore: log `window.set_shadow` errors

* chore: trigger CI

apps/app/package.json

@@ -9,7 +9,7 @@
     "fix": "cargo fmt && cargo clippy --fix"
   },
   "devDependencies": {
-    "@tauri-apps/cli": "2.1.0"
+    "@tauri-apps/cli": "2.5.0"
   },
   "dependencies": {
     "@modrinth/app-frontend": "workspace:*",