Auto-sync junctions on wire/symbol mutations

Replaces the manual add_schematic_junction tool with automatic junction
management. WireManager.sync_junctions inserts/removes junction dots
based on wire endpoints plus component pin positions and is invoked
after add_wire, add_polyline_wire, delete_wire, move, and rotate.

- Pin-aware: parses lib_symbols and applies KiCad's mirror/rotate/
  translate transform to compute world pin coordinates
- Multi-unit safe: filters lib_symbols sub-units by the placed
  symbol's (unit N) field plus the unit-0 common body
- Removes the now-unused WireManager.add_junction static method
- Updates CHANGELOG [Unreleased] with the tool removal notice
- Adds .mcp.json to .gitignore (machine-local paths)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

python/schemas/tool_schemas.py

@@ -1704,28 +1704,6 @@ SCHEMATIC_TOOLS = [
             "required": ["schematicPath", "outputPath"],
         },
     },
-    {
-        "name": "add_schematic_junction",
-        "title": "Add Junction to Schematic",
-        "description": "Adds a junction (connection dot) at the specified coordinates on the schematic. Junctions are required in KiCAD to mark intentional connections where wires cross or where a wire branches off another wire. Without a junction, crossing wires are not electrically connected.",
-        "inputSchema": {
-            "type": "object",
-            "properties": {
-                "schematicPath": {
-                    "type": "string",
-                    "description": "Path to schematic file",
-                },
-                "position": {
-                    "type": "array",
-                    "description": "The [x, y] coordinates where the junction should be placed. Must be on an existing wire intersection or branch point.",
-                    "items": {"type": "number"},
-                    "minItems": 2,
-                    "maxItems": 2,
-                },
-            },
-            "required": ["schematicPath", "position"],
-        },
-    },
     # --- Schematic Analysis Tools (read-only) ---
     {
         "name": "get_schematic_view_region",