feat: Feature 1.3 — Prop Analysis Engine with 6-step grading pipeline

Core intelligence for BetonBLK prop analysis:
- POST /api/analyze/prop — single prop analysis
- POST /api/analyze/batch — multi-prop analysis for parlay scanner
- 6-step pipeline: season avg → recent form → situational splits →
  cross-book lines → kill conditions → grade (A/B/C/D)
- 6 kill conditions: low_minutes, small_sample, b2b_high_usage,
  blowout_risk, split_conflict, no_opponent_data
- Composite scoring with confidence (30-95), bonuses, penalties
- Added spreads market to Odds API fetch (zero extra credits)
- Full reasoning output with step-by-step breakdown

36 new tests (unit + integration), 128 total across all features

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/oddsNormalizer.js

@@ -75,4 +75,44 @@ function normalizeProps(eventsWithOdds) {
   return props;
 }
 
-module.exports = { normalizeProps, MARKET_MAP, ALLOWED_BOOKS };
+function extractSpreads(eventsWithOdds) {
+  const spreads = [];
+
+  for (const event of eventsWithOdds) {
+    const homeTeam = getAbbreviation(event.home_team);
+    const awayTeam = getAbbreviation(event.away_team);
+    const gameTime = event.commence_time;
+
+    if (!Array.isArray(event.bookmakers)) continue;
+
+    for (const bookmaker of event.bookmakers) {
+      if (!ALLOWED_BOOKS.has(bookmaker.key)) continue;
+      if (!Array.isArray(bookmaker.markets)) continue;
+
+      for (const market of bookmaker.markets) {
+        if (market.key !== 'spreads') continue;
+        const outcomes = market.outcomes || [];
+
+        for (const outcome of outcomes) {
+          if (outcome.point == null) continue;
+          // Home team spread: outcome.name matches the team full name
+          if (outcome.name === event.home_team) {
+            spreads.push({
+              home_team: homeTeam,
+              away_team: awayTeam,
+              game_time: gameTime,
+              book: bookmaker.key,
+              home_spread: outcome.point,
+              fetched_at: market.last_update,
+            });
+            break;
+          }
+        }
+      }
+    }
+  }
+
+  return spreads;
+}
+
+module.exports = { normalizeProps, extractSpreads, MARKET_MAP, ALLOWED_BOOKS };

src/utils/signals.js

@@ -0,0 +1,15 @@
+function deltaToSignal(delta) {
+  const abs = Math.abs(delta);
+  if (abs < 0.5) return delta >= 0 ? 'neutral' : 'neutral';
+  if (abs < 2.0) return delta >= 0 ? 'lean' : 'lean_bearish';
+  if (abs < 4.0) return delta >= 0 ? 'bullish' : 'bearish';
+  return delta >= 0 ? 'strong_bullish' : 'strong_bearish';
+}
+
+function directedDelta(avg, line, direction) {
+  // For "over", positive delta is good. For "under", negative delta is good.
+  const raw = avg - line;
+  return direction === 'under' ? -raw : raw;
+}
+
+module.exports = { deltaToSignal, directedDelta };