feat(mcp): scaffold three project context tools

mcp_servers/project_context/providers/knowledge.py

@@ -0,0 +1,25 @@
+"""Provider boundary owned with search_project_knowledge."""
+
+from __future__ import annotations
+
+from typing import Any, Protocol
+
+from ..foundation import IdentityContext, ProviderError
+
+
+class KnowledgeProvider(Protocol):
+    def search_knowledge(self, **arguments: Any) -> dict[str, Any]: ...
+
+
+class UnconfiguredKnowledgeProvider:
+    def search_knowledge(self, **arguments: Any) -> dict[str, Any]:
+        raise ProviderError(
+            "UNAVAILABLE",
+            "The knowledge provider is not configured for this environment.",
+            retryable=False,
+        )
+
+
+def build_provider(identity: IdentityContext) -> KnowledgeProvider:
+    """Replace only this factory when wiring approved project retrieval."""
+    return UnconfiguredKnowledgeProvider()