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/services/nbaStatsClient.js

@@ -0,0 +1,48 @@
+const axios = require('axios');
+
+const NBA_SERVICE_URL = process.env.NBA_SERVICE_URL || 'http://localhost:8000';
+const TIMEOUT = 10000;
+
+async function getSeasonAvg(player, statType, season) {
+  const params = { player };
+  if (statType) params.stat_type = statType;
+  if (season) params.season = season;
+
+  const { data } = await axios.get(`${NBA_SERVICE_URL}/stats/season-avg`, {
+    params,
+    timeout: TIMEOUT,
+  });
+  return data;
+}
+
+async function getLastN(player, n = 10, statType) {
+  const params = { player, n };
+  if (statType) params.stat_type = statType;
+
+  const { data } = await axios.get(`${NBA_SERVICE_URL}/stats/last-n`, {
+    params,
+    timeout: TIMEOUT,
+  });
+  return data;
+}
+
+async function getSplits(player, statType, splitType, opponent) {
+  const params = { player, stat_type: statType, split_type: splitType };
+  if (opponent) params.opponent = opponent;
+
+  const { data } = await axios.get(`${NBA_SERVICE_URL}/stats/splits`, {
+    params,
+    timeout: TIMEOUT,
+  });
+  return data;
+}
+
+async function searchPlayer(name) {
+  const { data } = await axios.get(`${NBA_SERVICE_URL}/players/search`, {
+    params: { name },
+    timeout: TIMEOUT,
+  });
+  return data;
+}
+
+module.exports = { getSeasonAvg, getLastN, getSplits, searchPlayer };