fix: distinguish 404 in GetAllFilesInPath, make uploads idempotent

- Add APIError type with StatusCode field so callers can inspect HTTP
  status codes from Gitea API responses
- Add IsNotFound helper for ergonomic 404 checks
- GetAllFilesInPath now only falls back to single-file fetch on 404;
  all other errors (auth failures, server errors, rate limits) propagate
- Release workflow asset uploads are now idempotent: existing assets
  with the same name are deleted before re-upload on workflow re-runs

Closes #8
Closes #10

.gitea/workflows/release.yml

@@ -69,10 +69,24 @@ jobs:
 
           echo "Release ID: ${RELEASE_ID}"
 
-          # Upload each asset
+          # Upload each asset (idempotent: delete existing asset with same name first)
           for file in dist/*; do
             filename=$(basename "$file")
             echo "Uploading ${filename}..."
+
+            # Check if asset already exists and delete it
+            EXISTING_ID=$(curl -sS \
+              -H "Authorization: token ${GITEA_TOKEN}" \
+              "${GITEA_URL}/api/v1/repos/${REPO}/releases/${RELEASE_ID}/assets" \
+              | python3 -c "import json,sys; assets=json.load(sys.stdin); print(next((str(a['id']) for a in assets if a['name']=='${filename}'),''))" 2>/dev/null)
+
+            if [ -n "$EXISTING_ID" ]; then
+              echo "  Asset ${filename} already exists (id=${EXISTING_ID}), deleting..."
+              curl -sSf -X DELETE \
+                -H "Authorization: token ${GITEA_TOKEN}" \
+                "${GITEA_URL}/api/v1/repos/${REPO}/releases/${RELEASE_ID}/assets/${EXISTING_ID}"
+            fi
+
             curl -sSf -X POST \
               -H "Authorization: token ${GITEA_TOKEN}" \
               -H "Content-Type: application/octet-stream" \