Add Playwright E2E testing infrastructure

- Add playwright-web-flake to flake.nix for NixOS browser support
- Pin @playwright/test@1.56.1 to match nixpkgs version
- Create playwright.config.ts with Chromium-only, auto-start dev server
- Add e2e/smoke.spec.ts with initial smoke tests
- Add .mcp.json for Claude browser control via MCP
- Update .gitignore for playwright artifacts
- Remove E2E test skip from spec.md Known Limitations
- Update specs/testing.md to require three-tier testing approach

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.nix

@@ -2,11 +2,13 @@
 # ABOUTME: Provides Node.js 24, pnpm, turbo, lefthook, and Docker image output.
 {
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  inputs.playwright-web-flake.url = "github:pietdevries94/playwright-web-flake/1.56.1";
 
-  outputs = { nixpkgs, ... }:
+  outputs = { nixpkgs, playwright-web-flake, ... }:
     let
       system = "x86_64-linux";
       pkgs = nixpkgs.legacyPackages.${system};
+      playwright-driver = playwright-web-flake.packages.${system}.playwright-driver;
 
       # Custom Python package: garth (not in nixpkgs)
       garth = pkgs.python3Packages.buildPythonPackage {
@@ -48,32 +50,40 @@
       devShells.${system} = {
         # Default development shell with all tools
         default = pkgs.mkShell {
-          packages = commonPackages ++ (with pkgs; [
-            turbo
-            lefthook
-          ]);
+          packages = commonPackages ++ [
+            pkgs.turbo
+            pkgs.lefthook
+            playwright-driver
+          ];
 
           # For native modules (sharp, better-sqlite3, etc.)
           LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [ pkgs.stdenv.cc.cc ];
+
+          # Playwright browser configuration for NixOS (from playwright-web-flake)
+          PLAYWRIGHT_BROWSERS_PATH = "${playwright-driver.browsers}";
+          PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD = "1";
         };
 
         # Ralph sandbox shell with minimal permissions
         # Used for autonomous Ralph loop execution
         ralph = pkgs.mkShell {
-          packages = commonPackages ++ (with pkgs; [
-            # Claude CLI (assumes installed globally or via npm)
-            # Add any other tools Ralph needs here
-          ]);
+          packages = commonPackages ++ [
+            playwright-driver
+          ];
 
           # Restrictive environment for sandboxed execution
           shellHook = ''
             echo "🔒 Ralph Sandbox Environment"
-            echo "   Limited to: nodejs, pnpm, git"
+            echo "   Limited to: nodejs, pnpm, git, playwright"
             echo ""
           '';
 
           # For native modules
           LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [ pkgs.stdenv.cc.cc ];
+
+          # Playwright browser configuration for NixOS (from playwright-web-flake)
+          PLAYWRIGHT_BROWSERS_PATH = "${playwright-driver.browsers}";
+          PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD = "1";
         };
       };
     };