fix: downgrade upload-artifact to v3 for Gitea compatibility

The build was failing with:
  @actions/artifact v2.0.0+, upload-artifact@v4+ and download-artifact@v4+
  are not currently supported on GHES.

Gitea (self-hosted Git server) doesn't support the newer artifact actions
API used by v4. Downgraded all upload-artifact actions from v4 to v3.

Changed in 5 locations:
- API tests coverage upload
- Web tests coverage upload
- Shared tests coverage upload
- Build artifacts upload
- E2E test results upload

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitea/workflows/main.yml

@@ -88,7 +88,7 @@ jobs:
 
       - name: Upload coverage
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: api-coverage
           path: packages/api/coverage/
@@ -117,7 +117,7 @@ jobs:
 
       - name: Upload coverage
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: web-coverage
           path: packages/web/coverage/
@@ -143,7 +143,7 @@ jobs:
 
       - name: Upload coverage
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: shared-coverage
           path: packages/shared/coverage/
@@ -214,7 +214,7 @@ jobs:
         run: npm run build
 
       - name: Upload build artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: build-artifacts
           path: |
@@ -276,7 +276,7 @@ jobs:
 
       - name: Upload test results
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: playwright-report
           path: playwright-report/