Consolidate CI into single Project tests workflow

- Delete obsolete .gitea/workflows/nix.yml and rust.yml.
- Rename packages.yml to tests.yml.
- Add jobs check, nix, linux, aur with proper needs ordering.
- Update docs for new unified workflow.
- Remove bash and docker from flake.nix buildInputs.

flake.nix

@@ -59,9 +59,7 @@
       buildInputs = with pkgs; [
         rustToolchain
         alsa-lib
-        bash
         gitea-actions-runner
-        docker
       ];
       nativeBuildInputs = with pkgs; [pkg-config];
 
@@ -75,10 +73,7 @@
         echo "    nix run .#develop    - Run development version"
         echo ""
         echo "Gitea workflows:"
-        echo "    gitea-runner exec -W .gitea/workflows/rust.yml --event push -j check"
-        echo "    gitea-runner exec -W .gitea/workflows/nix.yml --event push -j build"
-        echo "    gitea-runner exec -W .gitea/workflows/packages.yml --event push -j linux"
-        echo "    gitea-runner exec -W .gitea/workflows/packages.yml --event push -j aur"
+        echo "    gitea-runner exec -W .gitea/workflows/tests.yml --event push --gitea-instance https://gitea.garandplg.com --network host"
       '';
     };
   };