Add exact source circuit validation to analog placement

[epowell40]

Summary

• add opt-in exact source electrical-system matching to room analog receptacle placement
• preserve source-unassigned devices explicitly and flag them for engineering review
• report factual panel, circuit, and before/after load receipts without making capacity or code-compliance claims
• harden the standalone circuit assignment route against label-only false positives

Verification

• 220 RevitBridge Common/Logic tests passed
• 9 focused deterministic backend tests passed
• RevitBridge net48 build passed (existing warnings only)
• live Revit 2024 Snowdon Room 403 preview and apply: 14/14 exact state matches, 13 assigned across seven P405 circuits, one source-unassigned state preserved
• GUI inspection in L4 - Power passed
• exact cleanup: 14 requested, 14 impacted, zero dependents; original circuit loads restored