feat: refactor to SI Quiz with Space Invaders arcade interface

- Updated Dockerfile to Python 3.11, selective COPY for cleaner image
- Expanded .gitignore with Python/OS patterns
- Added config.json, questions.json, env_example, and static assets
- Updated templates (host, player, scores) with Space Invaders UI
- Rewrote README for SI Quiz branding and setup docs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config.json

@@ -0,0 +1,25 @@
+{
+  "app_name": "SI Quiz",
+  "app_subtitle": "Space Invaders Quiz",
+  "org_name": "Your Team",
+  "host_password": "changeme",
+  "departments": [
+    "Engineering",
+    "Operations",
+    "IT",
+    "Sales",
+    "Finance",
+    "HR",
+    "Legal",
+    "Other"
+  ],
+  "time_limit_seconds": 30,
+  "questions_file": "questions.json",
+  "question_selection": {
+    "mode": "grouped",
+    "groups": [
+      { "tag": "general", "pick": 4 },
+      { "tag": "tool",    "pick": 1 }
+    ]
+  }
+}