Fix schematic syntax & finalize ERC

- Fixed: double-empty-string bug () in power symbol Footprint properties
- Fixed: single-line 67KB file was unparseable by KiCad - properly pretty-printed to 4408 lines
- Added: 42 no-connect flags for unused pins (J1 SBU, ESP32 GPIOs, NC resistors)
- Added: PWR_FLAG and GND power symbols connected to nets
- Added: batch_connect wiring for passives (C1-C5, R1-R7)
- Snap-to-grid: 152 elements aligned to 1.27mm grid
- Board sync: 13 footprints added, 16 nets confirmed
- Custom CH224K symbol verified and committed

USB_PD_ESP32S3.kicad_pro

@@ -310,7 +310,13 @@
     "bus_aliases": {},
     "legacy_lib_dir": "",
     "legacy_lib_list": [],
-    "top_level_sheets": []
+    "top_level_sheets": [
+      {
+        "filename": "USB_PD_ESP32S3.kicad_sch",
+        "name": "USB_PD_ESP32S3",
+        "uuid": "00000000-0000-0000-0000-000000000000"
+      }
+    ]
   },
   "sheets": [],
   "text_variables": {},