Add confidence_engine.py — deterministic, advisory, DB-free aggregator folding
per-component confidences + raw data-quality counts (deal/analog count,
domrf↔objective coverage, history months, confounded window) into one
High/Medium/Low via weakest-link MIN, capped at medium while advisory. Builds a
structural RU rationale naming the dragging factors with real numbers ("Low
потому что 7 сделок / 1 ЖК / покрытие 2.5%"). Fills the ReportConfidence slot of
#987 SiteFinderReport. 33 unit tests.
