fix: align production defaults and close review parity gaps

Ship greenfield min_rr=2.0 and conf=0, read-only Structural S/R, indicator
cache invalidation, and UI/gate language that treats GTL as screening not exit.
Align strategy_rank missing-vol fallback live vs backtest, single-source
PRIMARY_TARGET_MIN_RR, expand prod parity tests, and drop dead FE clients.

app/services/recommendation_service.py

@@ -618,6 +618,10 @@ def build_recommendation_snapshot(
 # agree on what counts as a probability-backed target.
 PRIMARY_TARGET_MIN_PROBABILITY = MIN_TARGET_PROBABILITY
 
+# Primary-target selector floor (independent of the live activation min_rr).
+# Live scanner and backtest setup replay must share this constant.
+PRIMARY_TARGET_MIN_RR = 1.5
+
 
 def _prune_floor_pinned_targets(targets: list[dict]) -> list[dict]:
     """Keep only the nearest target pinned at the probability clamp floor.