Label collision detection: resolve_label_collision() shifts different-net
labels that share the same (x,y) coordinate by 1.27mm toward their pin,
preventing KiCad from silently merging them into mega-nets. Integrated
at both label placement points in apply_batch.
Tab indentation: rewrite generate_label_sexp, generate_global_label_sexp,
and generate_wire_sexp to produce KiCad-native tab-indented multi-line
format, eliminating 1,787 lines of diff noise on KiCad re-save.
Intersheetrefs property now uses (at 0 0 0) placeholder.
Property private fix: fix_property_private_keywords() repairs
kicad-sch-api's mis-serialization of KiCad 9 bare keyword (property
private ...) as quoted (property "private" ...), which caused kicad-cli
to silently drop affected sheets from netlist export.
243 tests pass, ruff + mypy clean.
