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/routes/analyze.js

@@ -0,0 +1,79 @@
+const express = require('express');
+const { analyzeProp } = require('../services/propAnalyzer');
+
+const router = express.Router();
+
+const VALID_STAT_TYPES = new Set([
+  'points', 'rebounds', 'assists', 'threes', 'blocks',
+  'steals', 'pra', 'turnovers',
+]);
+
+const VALID_DIRECTIONS = new Set(['over', 'under']);
+
+function validateProp(prop) {
+  const errors = [];
+  if (!prop.player) errors.push('player is required');
+  if (!prop.stat_type) errors.push('stat_type is required');
+  if (prop.stat_type && !VALID_STAT_TYPES.has(prop.stat_type)) {
+    errors.push(`Invalid stat_type: ${prop.stat_type}`);
+  }
+  if (prop.line == null) errors.push('line is required');
+  if (!prop.direction) errors.push('direction is required');
+  if (prop.direction && !VALID_DIRECTIONS.has(prop.direction)) {
+    errors.push(`Invalid direction: ${prop.direction}`);
+  }
+  return errors;
+}
+
+router.post('/prop', async (req, res) => {
+  const errors = validateProp(req.body);
+  if (errors.length > 0) {
+    return res.status(400).json({ error: errors.join('; ') });
+  }
+
+  try {
+    const result = await analyzeProp(req.body);
+    return res.json(result);
+  } catch (err) {
+    if (err.response && err.response.status === 404) {
+      return res.status(404).json({ error: `Player not found: ${req.body.player}` });
+    }
+    if (err.statusCode === 429 || err.statusCode === 503) {
+      return res.status(err.statusCode).json({ error: err.message });
+    }
+    console.error('[BetonBLK] Analysis error:', err.message);
+    return res.status(503).json({ error: 'Analysis service temporarily unavailable' });
+  }
+});
+
+router.post('/batch', async (req, res) => {
+  const { props } = req.body;
+  if (!Array.isArray(props) || props.length === 0) {
+    return res.status(400).json({ error: 'props array is required and must not be empty' });
+  }
+
+  const results = [];
+  for (const prop of props) {
+    const errors = validateProp(prop);
+    if (errors.length > 0) {
+      results.push({ error: errors.join('; '), input: prop });
+      continue;
+    }
+
+    try {
+      const result = await analyzeProp(prop);
+      results.push(result);
+    } catch (err) {
+      results.push({
+        error: err.response?.status === 404
+          ? `Player not found: ${prop.player}`
+          : 'Analysis failed for this prop',
+        input: prop,
+      });
+    }
+  }
+
+  return res.json({ results });
+});
+
+module.exports = router;