docs(ci-gitea): replace '← upgraded from v3' with ADR-014 pin comment

Lines 203, 230, and 332 carried comments that actively encouraged
the regression (they read as if v4 is the canonical target). Replaced
with the correct pinned-at-v3 comment referencing ADR-014.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/infrastructure/ci-gitea.md

@@ -200,7 +200,7 @@ jobs:
         working-directory: frontend
       - name: Upload screenshots
         if: always()
-        uses: actions/upload-artifact@v4   # ← upgraded from v3
+        uses: actions/upload-artifact@v3  # pinned per ADR-014 — Gitea Actions does not implement v4 protocol. Do NOT upgrade.
         with:
           name: unit-test-screenshots
           path: frontend/test-results/screenshots/
@@ -227,7 +227,7 @@ jobs:
         working-directory: backend
       - name: Upload test results
         if: always()
-        uses: actions/upload-artifact@v4   # ← upgraded from v3
+        uses: actions/upload-artifact@v3  # pinned per ADR-014 — Gitea Actions does not implement v4 protocol. Do NOT upgrade.
         with:
           name: backend-test-results
           path: backend/target/surefire-reports/
@@ -329,7 +329,7 @@ jobs:
           E2E_BACKEND_URL: http://localhost:8080
       - name: Upload E2E results
         if: always()
-        uses: actions/upload-artifact@v4   # ← upgraded from v3
+        uses: actions/upload-artifact@v3  # pinned per ADR-014 — Gitea Actions does not implement v4 protocol. Do NOT upgrade.
         with:
           name: e2e-results
           path: frontend/test-results/e2e/