L2.1 FINAL v2: Clean routing + 60 GND vias + copper pours

- Restored board from commit 71dd98f (clean state before trace deletion)
- Imported best Freerouting SES: 277 tracks, 12 vias
- GND copper pours F.Cu+B.Cu, zone fill confirmed
- 60 GND stitching vias placed (collision-aware, none in U1 keepout)
- DRC: 140 violations (40 keepout + 21 via_dangling + 12 overlap + cosmetic)
- Gerbers v3 exported: gerbers-v3/ with 11 files
- JLCPCB DRC rules: 0.15mm clearance, 0.3mm min drill
- Netlist: 20 components, 17 nets, all connected

gerbers-v3/esp32-s3-sensor-node-Edge_Cuts.gm1

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