feat: refactor devshell as modular standalone path lol

devshells/web-bun.nix

@@ -0,0 +1,19 @@
+{ pkgs, ... }:
+
+pkgs.mkShell {
+  name = "web-bun";
+  packages = with pkgs; [
+    bun
+    nodejs_20
+    yarn
+    esbuild
+    vscode-langservers-extracted
+  ];
+  shellHook = ''
+    mkdir -p "$PWD/.cache/bun"
+    export BUN_INSTALL_CACHE="$PWD/.cache/bun"
+    echo "Bun/Node web shell ready"
+    echo "Bun: ${pkgs.bun.version}"
+    echo "Node: ${pkgs.nodejs_20.version}"
+  '';
+}