Fix username display issues (#6471)

# Description of Changes
Main fixes:
- Fix the display of the username in the bottom left
- Now displays as "User" when not logged in on self-hosted (desktop) and
"Guest" on SaaS when logged in anonymously
- Now updates properly when the user logs in/out in SaaS, desktop and
self-hosted
- Fix incremental build issues in the desktop app that have been here
since the start (I hope at least - I think the issue is that the JLink
is built read-only and then on subsequent builds you get OS errors when
trying to override the JLink with the new version. There's no real need
for it to be read-only that I know of, so we might as well just make it
R/W and ship like that)

.taskfiles/desktop.yml

@@ -133,8 +133,29 @@ tasks:
         --no-header-files
         --no-man-pages
         --output runtime/jre
+      # jlink emits its files mode 444 (read-only). Tauri's build-script
+      # resource copier preserves source permissions when staging
+      # `runtime/jre/**/*` into `target/<profile>/runtime/jre/...`, so the
+      # staged copies are read-only too. On any subsequent incremental
+      # build the copier tries to overwrite them and fails with a bare
+      # `Permission denied (os error 13)` (Rust's io::Error Display drops
+      # the path, so the failure is opaque). Make the source writable here
+      # so the staged destinations are writable and can be overwritten.
+      #
+      # Trade-off: this task runs for both `task desktop:dev` and
+      # `task desktop:build`, so production bundles also ship mode-644
+      # JRE files instead of 444. Functionally harmless on POSIX (the
+      # `other` bit is `r--` either way, and on macOS code signing is the
+      # real integrity check) and on Windows the DOS read-only attribute
+      # isn't load-bearing for the bundled JDK. If we ever need strict
+      # 444 in production, split the chmod into a dev-only step and have
+      # `desktop:build` run `jlink:clean` first to force a fresh build.
+      - cmd: chmod -R u+w runtime/jre
+        platforms: [linux, darwin]
+      - cmd: powershell -NoProfile -Command "Get-ChildItem -Recurse runtime/jre | ForEach-Object { $_.IsReadOnly = $false }"
+        platforms: [windows]
     status:
-      - test -d editor/src-tauri/runtime/jre
+      - test -f runtime/jre/release
 
   jlink:clean:
     desc: "Remove JLink runtime and bundled JARs"