Add minimalist web GUI for the v3.3.0 engine

Zero-dependency (stdlib http.server) front-end exposing only the essential
options — URL, backend, model, collaborator, RL + Playwright-MCP toggles — with
a live progress console. Calls neurosploit_agent directly; no npm/build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -81,3 +81,9 @@ results/
 
 # v3.3.0 runtime RL state
 data/rl_state.json
+
+# Playwright demo artifacts
+.playwright-mcp/
+neurosploit_gui_*.png
+neurosploit_demo_*.png
+logs/webgui.log