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.

compose.yaml

@@ -49,7 +49,7 @@ services:
         crond -f
 
   bot:
-    image: git.codeanddice.ru/toutsu/gmrelay-bot:3.9.3
+    image: git.codeanddice.ru/toutsu/gmrelay-bot:3.9.4
     restart: always
     depends_on:
       db:
@@ -67,7 +67,7 @@ services:
       retries: 3
 
   discord:
-    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:3.9.3
+    image: git.codeanddice.ru/toutsu/gmrelay-discord-bot:3.9.4
     restart: always
     depends_on:
       db:
@@ -86,7 +86,7 @@ services:
       retries: 3
 
   web:
-    image: git.codeanddice.ru/toutsu/gmrelay-web:3.9.3
+    image: git.codeanddice.ru/toutsu/gmrelay-web:3.9.4
     restart: always
     depends_on:
       db: