Add link management: create, select, delete with undo/redo

Implement full link workflow between component slots on the wiresheet:
- Link Mark / Link From / Link To context menu items for creating links
- Link dialog with slot type validation and source/target swap button
- Selectable link wires (click to highlight in red) with right-click delete
- Undo/redo support for both add and delete link operations
- Component deletion already cascades to remove related links

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

schema.py

@@ -161,6 +161,17 @@ def load_schema_kits_and_manifests():
     compile_schema_registry(manifest_paths)
 
 
+def get_all_slots_for_type(type_str):
+    """Returns every slot for a type as (name, type_string) tuples, for the link dialog."""
+    if type_str not in app_state.final_components_registry:
+        return []
+    return [
+        (slot["name"], slot["type"])
+        for slot in app_state.final_components_registry[type_str]
+        if slot["name"]
+    ]
+
+
 def get_slots_for_type(type_str, linked_slots=()):
     """
     Returns the slots worth painting for a given type, prefixed with double-digit