docs: add Gitea duplicate asset prevention pattern

Gitea silently appends duplicate asset names on re-triggered releases.
Added upload_asset helper that deletes existing assets before uploading.

gitea-python-ci-cd.md

@@ -168,6 +168,8 @@ build-docker:
 
 ### 2.3. Upload Assets to Gitea Release
 
+**IMPORTANT:** Gitea does not reject duplicate asset names — it silently appends duplicates. When re-triggering a failed release workflow (where `create-release` reuses an existing release), build jobs will upload a second copy of every artifact. Always **delete existing assets with the same name before uploading**.
+
 ```yaml
 - name: Attach assets to release
   env:
@@ -176,12 +178,31 @@ build-docker:
     RELEASE_ID="${{ needs.create-release.outputs.release_id }}"
     BASE_URL="${{ gitea.server_url }}/api/v1/repos/${{ gitea.repository }}"
 
+    upload_asset() {
+      local FILE="$1"
+      local NAME=$(basename "$FILE")
+
+      # Delete existing asset with the same name (prevents duplicates on re-run)
+      EXISTING_ID=$(curl -s "$BASE_URL/releases/$RELEASE_ID/assets" \
+        -H "Authorization: token $GITEA_TOKEN" \
+        | python3 -c "import sys,json; assets=json.load(sys.stdin); print(next((str(a['id']) for a in assets if a['name']=='$NAME'),''))" 2>/dev/null)
+
+      if [ -n "$EXISTING_ID" ]; then
+        curl -s -X DELETE "$BASE_URL/releases/$RELEASE_ID/assets/$EXISTING_ID" \
+          -H "Authorization: token $GITEA_TOKEN"
+        echo "Replaced existing asset: $NAME"
+      fi
+
+      curl -s -X POST \
+        "$BASE_URL/releases/$RELEASE_ID/assets?name=$NAME" \
+        -H "Authorization: token $GITEA_TOKEN" \
+        -H "Content-Type: application/octet-stream" \
+        --data-binary "@$FILE"
+      echo "Uploaded: $NAME"
+    }
+
     FILE=$(ls build/App-*.zip | head -1)
-    curl -s -X POST \
+    [ -f "$FILE" ] && upload_asset "$FILE"
-      "$BASE_URL/releases/$RELEASE_ID/assets?name=$(basename "$FILE")" \
-      -H "Authorization: token $GITEA_TOKEN" \
-      -H "Content-Type: application/octet-stream" \
-      --data-binary "@$FILE"
 ```
 
 ## 3. Version Detection Pattern