feat: initialization migration to Nuxt + Backend

This commit initializes both the Nuxt frontend and the Rust backend of
the new version of phundrak.com

backend/shell.nix

@@ -0,0 +1,77 @@
+{
+  inputs,
+  pkgs,
+  system,
+  self,
+  rust-overlay,
+  ...
+}: let
+  overlays = [(import rust-overlay)];
+  rustPkgs = import inputs.nixpkgs {inherit system overlays;};
+  rustVersion = rustPkgs.rust-bin.stable.latest.default;
+in
+  inputs.devenv.lib.mkShell {
+    inherit inputs pkgs;
+    modules = [
+      {
+        devenv.root = let
+          devenvRootFileContent = builtins.readFile "${self}/.devenv-root";
+        in
+          pkgs.lib.mkIf (devenvRootFileContent != "") devenvRootFileContent;
+      }
+      {
+        packages = with rustPkgs; [
+          (rustVersion.override {
+            extensions = [
+              "clippy"
+              "rust-src"
+              "rust-analyzer"
+              "rustfmt"
+            ];
+          })
+          bacon
+          cargo-deny
+          cargo-shuttle
+          cargo-tarpaulin
+          cargo-watch
+          flyctl
+          just
+          tombi # TOML lsp server
+          vscode-langservers-extracted
+        ];
+
+        services.mailpit = {
+          enable = true;
+          # HTTP interface for viewing emails
+          uiListenAddress = "127.0.0.1:8025";
+          # SMTP server for receiving emails
+          smtpListenAddress = "127.0.0.1:1025";
+        };
+
+        processes.run.exec = "cargo watch -x run";
+
+        enterShell = ''
+          echo "🦀 Rust backend development environment loaded!"
+          echo "📦 Rust version: $(rustc --version)"
+          echo "📦 Cargo version: $(cargo --version)"
+          echo ""
+          echo "Available tools:"
+          echo "  - rust-analyzer (LSP)"
+          echo "  - clippy (linter)"
+          echo "  - rustfmt (formatter)"
+          echo "  - bacon (continuous testing/linting)"
+          echo "  - cargo-deny (dependency checker)"
+          echo "  - cargo-tarpaulin (code coverage)"
+          echo ""
+          echo "📧 Mailpit service:"
+          echo "  - SMTP server: 127.0.0.1:1025"
+          echo "  - Web UI: http://127.0.0.1:8025"
+          echo ""
+          echo "🚀 Quick start:"
+          echo "  Run 'devenv up' to launch:"
+          echo "    - Mailpit service (email testing)"
+          echo "    - Backend with 'cargo watch -x run' (auto-reload)"
+        '';
+      }
+    ];
+  }