tools/epro2/kicad: fix two structural ERC bugs — wire_dangling -88%, pin_not_connected -52%

Bisect found two semantics mismatches between EPRO2 and KiCad that cause
the 850 real-connectivity ERC violations on the ESP-VoCat ref project:

1. sym_writer was emitting lib coords without negating Y, but KiCad lib
   uses Y-up and re-flips Y on placement (Y-down schematic). So vertically
   arranged pins ended up at Y-mirrored absolute positions and wires that
   reach the geometric pin tip in EPRO2 missed the rendered pin tip in
   KiCad. Fix: lib_y = -epro2_y, lib_rot = (360 - rot) % 360 for pin/text.

2. sch_writer was treating each LINE as an isolated wire — but EPRO2
   binds segments into nets by NAME (WIRE.NET attr), not just geometry.
   Multi-segment nets like GND/VBUS show up as N disconnected stubs to
   KiCad. Fix: per-LINE, look up lineGroup → WIRE → NET attr and emit a
   `(label "<NET>")` at the LINE's start. Same-named labels on distinct
   physical wires is how KiCad's ERC recognizes a multi-segment net.

ESP-VoCat 9 sheets:
  wire_dangling           444 →  52  (-88%)
  pin_not_connected       406 → 196  (-52%)
  real connectivity total 850 → 248  (-71%)

Why we did NOT round to grid (the obvious-looking fix): EPRO2 places
some pins on a 10-mil pitch (e.g. magnetic socket); rounding to KiCad's
default 50-mil ERC grid would collapse those pins. The 248 residual is
fundamentally cross-sheet — single-sheet ERC can't see a net's other
endpoints on sibling sheets — and is a Phase-3 (hierarchical sheet)
problem, not a per-sheet one.

41 → 46 unit tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tools/epro2/kicad/__main__.py

@@ -51,7 +51,7 @@ def _convert_one(
     if stats:
         print(
             f"  {out_path.name}: wires={stats.wires} symbols={stats.symbol_placements} "
-            f"text={stats.text} skipped={stats.skipped} "
+            f"text={stats.text} labels={stats.labels} skipped={stats.skipped} "
             f"lib_emb={stats.lib_symbols_embedded} lib_miss={stats.lib_symbols_missing}"
         )
     return out_path