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>

src/tools/registry.ts

@@ -94,7 +94,6 @@ export const toolCategories: ToolCategory[] = [
       "annotate_schematic",
       "add_schematic_wire",
       "delete_schematic_wire",
-      "add_schematic_junction",
       "add_schematic_net_label",
       "delete_schematic_net_label",
       "connect_to_net",