chore: bump version 3.9.3 -> 3.9.4

Test-only patch release. Sync the four canonical version sources:
- Directory.Build.props
- compose.yaml (bot, discord, web image tags)
- .gitea/workflows/deploy.yml (VERSION env)
- src/GmRelay.Web/Components/Layout/NavMenu.razor (visible nav-version)

The new NavMenu_ShouldExposeCurrentProjectVersion test reads the
version from Directory.Build.props, so this bump does NOT need a
hand-edited test literal — verified locally that the test passes
on 3.9.4 with no manual changes.

.gitea/workflows/deploy.yml

@@ -6,7 +6,7 @@ on:
       - main 
 
 env:
-  VERSION: 3.9.3
+  VERSION: 3.9.4
 
 jobs:
   # ЧАСТЬ 1: Собираем образы и кладем в Gitea (чтобы делиться с ребятами)