fix: point mcp.json at the real MCP endpoint + replace stale tool docs

- mcp.json: bare https://mcp.spaghetti.gg ->
  https://mcp.spaghetti.gg/api/mcp/agentic-engine/mcp (the host root does
  not serve MCP; Caddy proxies the whole host without a path rewrite)
- SKILL.md/README: replace tools that no longer exist (analyze_crash,
  audit_assets, search_kb) with the shipped set (analyze_logs,
  tidy_assets, make_tool, topup, the five research tools); document
  credit costs and the approval flow
- drop stale claims: GoTrue, spaghetti.gg/dashboard, tm_/prj_ id
  prefixes, '.spaghetti auto-created on first tool call' (unimplemented)
- plugin.json: 0.1.0 -> 0.1.1

plugin.json

@@ -1,8 +1,8 @@
 {
   "$schema": "https://agent-plugins.org/schemas/1.0.0/plugin.schema.json",
   "name": "unreal-workbench",
-  "version": "0.1.0",
-  "description": "Unreal Engine 5 agent tools — crash analysis, asset auditing, knowledge base, code generation. Powered by Spaghetti Unreal AI Workbench.",
+  "version": "0.1.1",
+  "description": "Unreal Engine 5 agent tools — log analysis, asset auditing, engine docs research, script generation. Powered by Spaghetti Unreal AI Workbench.",
   "author": {
     "name": "Tinirau Ltd",
     "url": "https://spaghetti.gg"