fix(nix): make hermes in developement environment actually work

install modules as editable overlay with uv

nix/devShell.nix

@@ -28,13 +28,20 @@
         packages =
           with pkgs;
           [
+            (pkgs.runCommand "hermes" { } ''
+              mkdir -p $out/bin
+              install -Dm755 ${../hermes} $out/bin/hermes
+            '')
             uv
           ]
           ++ self'.packages.default.passthru.devDeps;
         shellHook = ''
-          echo "Hermes Agent dev shell"
           ${combinedNonNpm}
           ${hermesNpmLib.mkNpmDevShellHook npmPackageJsonPaths}
+
+          # for the devshell to pick up the src
+          export HERMES_PYTHON_SRC_ROOT=$(git rev-parse --show-toplevel)
+          echo "Hermes Agent dev shell in $HERMES_PYTHON_SRC_ROOT"
           echo "Ready. Run 'hermes' to start."
         '';
       };