Unified, portable Unreal Engine MCP system plugin

Merge of the two project copies into one self-contained plugin (the superset:
variable_op + variables.py, full pcg_op runtime/declarative/preset ops, the
CreateWidgetFloatAnimation widget tool, and full Voxel graph authoring).

Made fully project- and machine-agnostic — no hardcoded paths:
- New src/projectPaths.js auto-detects the host .uproject (walk-up), project
  name, Editor build target, log file, and engine install (EngineAssociation
  via launcher manifest/registry, else installed-engine scan). All overridable
  via UE_* env vars.
- Rewired buildOrchestrator/insights/launcher/insightsExporter/server.js and the
  Python workers (cpp_scaffold, live_coding, apply_graph, console) off the old
  C:/Github/ihy, IHY*, E:/UE_Versions and UE_5.7 literals onto the resolver.
- Voxel made optional: Build.cs auto-detects the Voxel plugin (env
  UE_MCP_WITH_VOXEL override) and the C++ compiles to stubs under WITH_MCP_VOXEL,
  so the module builds in projects without Voxel; .uplugin marks Voxel optional.
- De-branded the agent-gateway and docs; scrubbed a leaked API key; excluded
  node_modules/Binaries/Intermediate/__pycache__/secrets from the repo.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -74,3 +74,20 @@ Plugins/**/Intermediate/*
 # Cache files for the editor to use
 DerivedDataCache/*
 
+# ---> MCP server / Node.js
+node_modules/
+npm-debug.log*
+yarn-error.log*
+
+# ---> Python workers
+__pycache__/
+*.pyc
+
+# ---> Secrets & local config (NEVER commit these)
+# auth token for the agent gateway — copy auth.env.example to auth.env locally
+auth.env
+agent-gateway/auth.env
+agent-gateway/.generated-audio/
+# real API keys live in a local, untracked copy
+integrations.local.json
+