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

untitled-erc.rpt

@@ -0,0 +1,12 @@
+ERC report (2026-06-20T17:36:22, Encoding UTF8)
+Report includes: Errors, Warnings
+
+***** Sheet /
+
+ ** ERC messages: 0  Errors 0  Warnings 0
+
+ ** Ignored checks:
+    - Global label only appears once in the schematic
+    - Four connection points are joined together
+    - SPICE model issue
+    - Assigned footprint doesn't match footprint filters