Fix REPEAT local net labels collapsing distinct rails across rooms

[cs42]

Summary

• Local schematic net names on REPEAT sheets (e.g. P_IN) were used as a global rail-group alias, so unconnected PCB nets (P_IN.1, P_IN.2, …) were merged into one mega-rail in the Rails list / topology / copper eyes.
• Alias-union requested_net ↔ pin nets only when every terminal sharing that label resolves onto shared copper; REPEAT labels with disjoint pin nets stay display-only. Per-instance SERIES bridges and unique local→canonical aliases (e.g. 5V_LOCAL → +5V) are unchanged.
• Caploop rail membership follows the same rule so a shared local name cannot match every room’s rail.

Motivation

Users correctly annotate child sheets with local names (PDN_P_NET=P_IN), not flattened PCB names. The solver already resolved terminals per instance, but the rail grouper treated the bare local string as one net identity. That made multi-motor / multi-channel designs look shorted in the UI even when copper and the FEM were separate — and hid the per-instance rails people expect after modelling drivers as REGULATORs.

Test plan

• pytest tests/test_rails.py tests/test_rail_trees.py tests/test_caploop_identify.py
• On a REPEAT design: two SERIES instances with the same local P_IN/P_OUT → two rails, members only within each room
• REGULATOR outs with shared local P_IN1 and shared VDD_MOTOR in → separate OUT rails, one IN rail
• Existing local-alias case (5V_LOCAL → +5V) still groups and nests correctly