Add GitHub Actions workflow for building and uploading linux_amd64 extension

.github/workflows/build-linux-amd64.yml

@@ -0,0 +1,32 @@
+name: Build linux_amd64 extension and upload to Packages
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: Package version (defaults to tag name or short SHA)
+        required: false
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  build-linux-amd64:
+    runs-on: ubuntu-latest
+    env:
+      EXTENSION_NAME: ui
+      DUCKDB_PLATFORM: linux_amd64
+    steps:
+      - name: Install build dependencies
+        run: |
+          set -e
+          export DEBIAN_FRONTEND=noninteractive
+          apt-get update
+          apt-get install -y --no-install-recommends \
+            build-essential cmake ninja-build python3 python3-venv pkg-config \
+            libssl-dev curl git ca-certificates
+# ... submodule init, build release, find artifact ...
+      - name: Upload to Gitea Packages (generic)
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+        run: |
+          curl -fsSL -X PUT -H "Authorization: token ${GITEA_TOKEN}" -H "Content-Type: application/octet-stream" --upload-file "$file" "$server/api/packages/$owner/generic/$pkg/$version/$name?replace=1"