cargoxx-pkgs registry skeleton

Empty package registry for cargoxx. flake.nix walks
recipes/<name>/versions/*.toml, exposes each (name, version) as
packages.<system>.{<name>_<safe_ver>, <name>}, and builds via
cargoxx.lib.${system}.buildCppPackage with pkgs.fetchgit.

.gitea/workflows/validate-pr.yml validates schema, refetches and verifies
source sha256, smoke-builds, pushes $out to the binary cache, and labels
auto-merge once the PR author is in maintainers.txt.

.gitea/workflows/auto-merge.yml merges via tea on the auto-merge label.

.gitea/workflows/auto-merge.yml

@@ -0,0 +1,19 @@
+name: auto-merge
+
+on:
+  pull_request:
+    types: [labeled]
+
+jobs:
+  merge:
+    if: github.event.label.name == 'auto-merge'
+    runs-on: self-hosted
+    steps:
+      - name: merge
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+        run: |
+          tea pr merge \
+            --repo "${{ github.repository }}" \
+            --style squash \
+            "${{ github.event.pull_request.number }}"