Return pointers from Materialize to avoid struct copies

Change Materialize() to return []*ServerTool instead of []ServerTool.
This avoids copying the entire ServerTool struct (which includes the
JSON schema) for each tool in the result.

Benchmark improvement:
- Materialize: 6199ns → 1114ns (5.6x faster)
- Memory: 12584B → 472B (27x less)
- Allocations: 4 → 3

The returned pointers reference the cached tools in the index.
Callers must not modify them.

Author: SamMorrowDrums

pkg/inventory/tool_index.go

@@ -216,14 +216,15 @@ func (idx *ToolIndex) GetToolByName(name string) (*ServerTool, int, bool) {
 
 // Materialize converts a QueryResult into actual tools, running dynamic checks as needed.
 // Only tools in NeedsDynamicCheck have their Enabled() function called.
-func (idx *ToolIndex) Materialize(ctx context.Context, qr QueryResult) []ServerTool {
+// Returns pointers to the cached tools - callers should NOT modify them.
+func (idx *ToolIndex) Materialize(ctx context.Context, qr QueryResult) []*ServerTool {
 	// Pre-allocate with capacity = guaranteed + potential dynamic
 	capacity := qr.Guaranteed.PopCount() + qr.NeedsDynamicCheck.PopCount()
-	result := make([]ServerTool, 0, capacity)
+	result := make([]*ServerTool, 0, capacity)
 
 	// Add all guaranteed tools (no dynamic check needed)
 	qr.Guaranteed.Iterate(func(pos int) bool {
-		result = append(result, idx.tools[pos])
+		result = append(result, &idx.tools[pos])
 		return true
 	})
 
@@ -236,7 +237,7 @@ func (idx *ToolIndex) Materialize(ctx context.Context, qr QueryResult) []ServerT
 				return true // skip this tool, continue iteration
 			}
 		}
-		result = append(result, *tool)
+		result = append(result, tool)
 		return true
 	})