docs: initialize NixOS infrastructure with AI assistant

Creates PROJECT.md with vision and requirements.
Creates config.json with interactive workflow mode.

.planning/config.json

@@ -0,0 +1,17 @@
+{
+  "mode": "interactive",
+  "gates": {
+    "confirm_project": true,
+    "confirm_phases": true,
+    "confirm_roadmap": true,
+    "confirm_breakdown": true,
+    "confirm_plan": true,
+    "execute_next_plan": true,
+    "issues_review": true,
+    "confirm_transition": true
+  },
+  "safety": {
+    "always_confirm_destructive": true,
+    "always_confirm_external_services": true
+  }
+}