Add bounded live retention for UI and API caches

- Introduce configurable hot-window and pinned evidence retention
- Keep live evidence available after eviction with fetch-on-miss hydration
- Add tests and docs for the new retention settings

.env.example

@@ -57,6 +57,9 @@ COMPUTE_DELIVER_POLICY=new
 COMPUTE_CONSUMER_RESET=false
 NBBO_MAX_AGE_MS=1000
 NEXT_PUBLIC_NBBO_MAX_AGE_MS=1000
+NEXT_PUBLIC_LIVE_HOT_WINDOW=2000
+NEXT_PUBLIC_PINNED_EVIDENCE_TTL_MS=1200000
+NEXT_PUBLIC_PINNED_EVIDENCE_MAX_ITEMS=4000
 ROLLING_WINDOW_SIZE=50
 ROLLING_TTL_SEC=86400
 CLASSIFIER_SWEEP_MIN_PREMIUM=40000
@@ -81,3 +84,13 @@ REPLAY_END_TS=0
 REPLAY_SPEED=1
 REPLAY_BATCH_SIZE=200
 REPLAY_LOG_EVERY=1000
+
+# API live retention (generic channels)
+LIVE_LIMIT_OPTIONS=10000
+LIVE_LIMIT_NBBO=10000
+LIVE_LIMIT_EQUITIES=10000
+LIVE_LIMIT_EQUITY_JOINS=10000
+LIVE_LIMIT_FLOW=10000
+LIVE_LIMIT_CLASSIFIER_HITS=10000
+LIVE_LIMIT_ALERTS=10000
+LIVE_LIMIT_INFERRED_DARK=10000