[verified] Add capital-allocation simulation engine + MT5 bridge (both dry-run/gated)

- simulation.py: price-series loader (Yahoo snapshot) + allocate_capital 50/20/30 with min-100 shares, bucket3 excludes bucket1, cash fallback
- /api/v1/simulation POST: combines theme 60/40 score + Siamchart dividend + Yahoo price; labels output paper/backtest non-PIT (never validated)
- mt5_bridge.py: MT5 order interface, dry-run default; live dispatch needs MT5_SEND_ORDERS=1 AND approval (Windows-only MetaTrader5)
- 12 new tests (simulation/mt5/api); full suite 184 OK; live verified (1M -> buckets)

backend/tests/test_simulation.py

@@ -0,0 +1,72 @@
+"""Tests for the capital-allocation simulation engine."""
+
+from __future__ import annotations
+
+import unittest
+
+from app.simulation import Candidate, allocate_capital
+
+
+class AllocationTest(unittest.TestCase):
+    def make_candidates(self):
+        # dividend + high score
+        return [
+            Candidate("A", 10.0, 1.5, True, 5.0),
+            Candidate("B", 20.0, 1.2, True, 3.0),
+            Candidate("C", 5.0, 1.0, False, 0.0),
+            Candidate("D", 2.0, 0.5, False, 0.0),
+            Candidate("E", 50.0, 0.9, True, 8.0),
+        ]
+
+    def test_allocates_three_buckets(self):
+        res = allocate_capital(200_000, self.make_candidates())
+        bucket_notional = res.bucket_notional
+        self.assertIn(1, bucket_notional)
+        self.assertIn(2, bucket_notional)
+        self.assertIn(3, bucket_notional)
+        # total invested + unallocated == capital
+        self.assertAlmostEqual(res.invested + res.unallocated_cash, 200_000, places=2)
+        # every order is a multiple of 100
+        for o in res.orders:
+            self.assertEqual(o.qty % 100, 0)
+            self.assertGreaterEqual(o.qty, 100)
+
+    def test_min_100_shares_respected(self):
+        # tiny capital: bucket1 50% still must afford 100 shares
+        res = allocate_capital(2_000, self.make_candidates())
+        for o in res.orders:
+            self.assertGreaterEqual(o.qty, 100)
+            self.assertEqual(o.notional, o.qty * o.price)
+        # never over-invest beyond capital
+        self.assertLessEqual(res.invested, 2_000)
+
+    def test_bucket3_excludes_already_bought(self):
+        cands = [Candidate("A", 10.0, 1.5, True, 5.0),
+                 Candidate("B", 10.0, 0.1, True, 8.0)]
+        res = allocate_capital(300_000, cands)
+        # A (bought in bucket1) must NOT also appear in bucket3
+        bucket3_syms = [o.symbol for o in res.orders if o.bucket == 3]
+        bucket1_syms = [o.symbol for o in res.orders if o.bucket == 1]
+        overlap = set(bucket3_syms) & set(bucket1_syms)
+        self.assertEqual(overlap, set())
+
+    def test_invalid_capital_raises(self):
+        with self.assertRaises(Exception):
+            allocate_capital(0, self.make_candidates())
+        with self.assertRaises(Exception):
+            allocate_capital(-100, self.make_candidates())
+
+    def test_no_candidates_raises(self):
+        with self.assertRaises(Exception):
+            allocate_capital(100_000, [])
+
+    def test_cash_fallback_when_nothing_fits(self):
+        # only very high-priced names, tiny capital -> cannot buy 100 shares -> cash
+        cands = [Candidate("X", 1000.0, 2.0, True, 3.0)]
+        res = allocate_capital(50_000, cands)  # 50% = 25k, can't buy 100*1000
+        self.assertEqual(res.orders, [])
+        self.assertAlmostEqual(res.unallocated_cash, 50_000, places=2)
+
+
+if __name__ == "__main__":
+    unittest.main()