feat(schematic): add list_symbol_pins to read pins from symbol libraries

Adds list_symbol_pins and batch_list_symbol_pins: read a symbol's pin
number/name/type/local-position straight from the .kicad_sym libraries,
without placing it on a schematic. Fills a gap in library_symbol.py
(which can search/list symbols and read properties but not pins) and
complements get_schematic_pin_locations (placed-symbol coords only).

- python/commands/symbol_pins.py: SymbolPinCommands (stateless)
- src/tools/library-symbol.ts: tool wrappers; registry 'symbol_pins' category
- python/kicad_interface.py: import + instantiate + dispatch routes
- tests/test_symbol_pins.py: 12 unit tests (MagicMock loader; no system KiCad)

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

src/tools/registry.ts

@@ -118,6 +118,11 @@ export const toolCategories: ToolCategory[] = [
     description: "Footprint library access: search, browse, get footprint information",
     tools: ["list_libraries", "search_footprints", "list_library_footprints", "get_footprint_info"],
   },
+  {
+    name: "symbol_pins",
+    description: "Read a symbol's pins straight from the library (no schematic needed)",
+    tools: ["list_symbol_pins", "batch_list_symbol_pins"],
+  },
   {
     name: "routing",
     description: "Advanced routing operations: vias, copper pours",