feat: adopt Phase 3 gate and paper-trade exit policy

Production strategy change based on the July 2026 backtest: paper trades now default to a 30-trading-day hold with the initial stop (classic momentum hold-and-rerank), while target and trailing exits remain available in Admin. The exit policy API/UI now carries hold_days and close_reason can be 'time'.

The activation confidence floor default is now 0/off because the gate ablation showed it added no per-trade edge while filtering out usable setups. Migration 015 clears stored activation_min_confidence and paper_exit_mode so the new defaults take effect; this intentionally resets Track Record comparability from this deploy.

Verification: 451 backend tests pass, ruff check app/ clean, frontend npm run build clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -15,7 +15,7 @@ Once a day (default 07:00). Steps run **in dependency order**, each consuming th
 1. **OHLCV** — fetch the latest daily bars for every tracked ticker (Alpaca); new tickers backfill ~5 years.
 2. **Sentiment** — fetch sentiment for the names that matter and are stale (> 5 days): top-pick feeders (momentum leaders with a tradeable long setup), the watchlist, and open paper trades, plus a top-N-by-composite discovery net. Runs *before* the scan so the scan sees fresh sentiment.
 3. **R:R Scan** — recompute S/R zones, the 5-dimension scores and long/short setups (ATR stops, S/R targets) for every ticker, and attach each ticker's 12‑1 momentum percentile.
-4. **Outcome Eval** — resolve setups that hit target/stop or expired (default 30 trading days) and close paper trades that hit a level.
+4. **Outcome Eval** — resolve setups that hit target/stop or expired (default 30 trading days) and auto-close paper trades per the exit policy (default: hold 30 trading days with the initial stop — the backtest-validated exit).
 5. **Market Regime** — recompute the regime index (breadth/trend).
 6. **Regime Monitor** — observational early-warning snapshot (VIX, credit spreads via FRED); feeds nothing else.
 
@@ -33,7 +33,7 @@ Fundamentals (weekly, early Monday) · Alerts (hourly, Telegram) · Backtest (we
 
 1. **Composite score** — technical, S/R-quality, sentiment, fundamental and momentum sub-scores (0–100) combine into a weighted composite (weights configurable; missing dimensions re-normalize).
 2. **Setups** — the scanner builds long/short setups with ATR stops and S/R targets, then adds a confidence score, conflict flags and a target reach-probability.
-3. **Activation gate** — a setup *qualifies* only if it clears the R:R and confidence floors **and** ranks in the top momentum percentile of the universe (the validated edge is long-only momentum).
+3. **Activation gate** — a setup *qualifies* only if it clears the R:R floor **and** ranks in the top momentum percentile of the universe (the validated edge is long-only momentum; the confidence floor was ablated to zero effect and defaults off).
 4. **Top pick** — the highest-momentum qualified setup; highlighted on the Dashboard and labelled on the ticker page.
 
 ## Strategy Status — What's Validated and What Isn't
@@ -102,9 +102,9 @@ Corollaries: never let an unvalidated score gate setups; the outcome evaluator m
 - Fundamental data tracking (P/E, revenue growth, earnings surprise, market cap)
 - 5-dimension scoring engine (technical, S/R quality, sentiment, fundamental, momentum) with configurable weights
 - Risk:Reward scanner — long and short setups, ATR-based stops, S/R-based targets, configurable R:R threshold (default 1.5:1)
-- Activation gate — qualifies setups on a momentum-percentile floor plus R:R/confidence (validated long-only edge); ranks the rest by expected value
+- Activation gate — qualifies setups on a momentum-percentile floor plus an R:R floor (validated long-only edge)
 - Recommendation layer — directional confidence, conflict detection, per-target reach-probability
-- Paper trading — take a setup, mark-to-market vs. latest close, auto-close on stop/target, realized track record + outcome evaluation
+- Paper trading — take a setup, mark-to-market vs. latest close, auto-close per the exit policy (default: hold 30 trading days with the initial stop; trailing / target-stop selectable), realized track record + outcome evaluation
 - Market-regime index + FRED early-warning monitor (VIX, credit spreads); weekly backtest + manual event study
 - Telegram alerts (e.g. regime-quadrant changes)
 - User-curated watchlist (cap: 20), enriched with composite score, R:R and S/R summary