docs: document and configure MCP tool integration

- Create comprehensive MCP.md documenting all available tools:
  * Hugging Face Hub (models, datasets, papers, spaces, docs)
  * Web search and fetch for research
  * Code tools (Bash, Git, file ops)
  * Claude Code (GSD) workflow agents

- Map MCP usage to specific phases:
  * Phase 1: Model discovery (Mistral, Llama, quantized options)
  * Phase 2: Safety research (sandboxing, verification papers)
  * Phase 5: Conversation datasets and papers
  * Phase 12: Voice visualization models and spaces
  * Phase 13: Avatar generation tools and research
  * Phase 14: Mobile inference frameworks and patterns

- Update config.json with MCP settings:
  * Enable Hugging Face (mystiatech authenticated)
  * Enable WebSearch for current practices
  * Set default result limits

- Update PROJECT.md constraints to document MCP enablement

Research phases will leverage MCPs extensively for optimal
library/model selection, architecture patterns, and best practices.

.planning/config.json

@@ -13,5 +13,27 @@
     "auto_push": true,
     "push_tags": true,
     "remote": "master"
+  },
+  "mcp": {
+    "huggingface": {
+      "enabled": true,
+      "authenticated_user": "mystiatech",
+      "default_result_limit": 10,
+      "use_for": [
+        "model_discovery",
+        "dataset_research",
+        "paper_search",
+        "documentation_lookup"
+      ]
+    },
+    "web_research": {
+      "enabled": true,
+      "use_for": [
+        "current_practices",
+        "library_research",
+        "architecture_patterns",
+        "security_best_practices"
+      ]
+    }
   }
 }