build: seed APP_VERSION and API_KEY from the environment

Fresh cmake configures pick up APP_VERSION/API_KEY from environment
variables (as nix develop and CI provide them); -D still wins on
reconfigure. Also normalizes indentation in the sd-bus blocks.

flake.nix

@@ -39,8 +39,20 @@
             devShells.default = pkgs.mkShell {
               inputsFrom = [ self.packages.${system}.default ];
               packages = [ ];
+              env = {
+                # APP_VERSION and API_KEY are CMake cache variables with no
+                # default; on a fresh configure cmake seeds their cache from
+                # environment variables of the same name, so a plain
+                # `cmake -S . -B build` bakes them into the binary.
+                APP_VERSION = "dev";
+              };
               shellHook = ''
-                echo "RadiantWave dev shell"
+                # Never commit the real key. Export API_KEY (or the CI name
+                # RWT_LIVE_API_KEY) in your ambient environment and this shell
+                # picks it up; empty by default (no auth header).
+                export API_KEY="''${API_KEY:-''${RWT_LIVE_API_KEY:-}}"
+
+                echo "RadiantWave dev shell (APP_VERSION=dev, API_KEY=$([[ -n "$API_KEY" ]] && echo set || echo unset))"
                 echo "  Configure: cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Debug"
                 echo "  Build:     cmake --build build"
                 echo "  Run:       ./build/radiantwave"