feat(schematic): hierarchical sheet insertion and subsheet scaffolding

Adds add_hierarchical_sheet (insert a sheet symbol referencing a child
.kicad_sch, with sheet_instances + fixed component instance paths) and
create_hierarchical_subsheet (create the child file + wire it into the parent
in one call). Upstream has add_sheet_pin / add_schematic_hierarchical_label
but no way to create a sheet or stand up a child sheet, so hierarchical
designs can't be built through the MCP server today.

- python/commands/schematic_hierarchy.py: SchematicHierarchyCommands
- src/tools/schematic-hierarchy.ts + registry 'schematic_hierarchy' category
- python/kicad_interface.py: import + instantiate + dispatch routes
- tests/test_schematic_hierarchy.py: 5 unit/integration tests on real .kicad_sch

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

src/server.ts

@@ -20,6 +20,7 @@ import { registerExportTools } from "./tools/export.js";
 import { registerSchematicTools } from "./tools/schematic.js";
 import { registerLibraryTools } from "./tools/library.js";
 import { registerSymbolLibraryTools } from "./tools/library-symbol.js";
+import { registerSchematicHierarchyTools } from "./tools/schematic-hierarchy.js";
 import { registerJLCPCBApiTools } from "./tools/jlcpcb-api.js";
 import { registerDatasheetTools } from "./tools/datasheet.js";
 import { registerFootprintTools } from "./tools/footprint.js";
@@ -296,6 +297,7 @@ export class KiCADMcpServer {
     registerSchematicTools(this.server, this.callKicadScript.bind(this));
     registerLibraryTools(this.server, this.callKicadScript.bind(this));
     registerSymbolLibraryTools(this.server, this.callKicadScript.bind(this));
+    registerSchematicHierarchyTools(this.server, this.callKicadScript.bind(this));
     registerJLCPCBApiTools(this.server, this.callKicadScript.bind(this));
     registerDatasheetTools(this.server, this.callKicadScript.bind(this));
     registerFootprintTools(this.server, this.callKicadScript.bind(this));