feat(economy): add /bank vault (rob-proof storage) + net-worth leaderboard

A strategic counterpart to /rob: coins moved to the bank are safe from /rob and
/heist (which only touch liquid balance) but earn no Bot Farm interest and can't
be spent, gambled or given until withdrawn - the deliberate trade-off against
keeping coins liquid.

- New bank.py (do_deposit/do_withdraw), bank_balance schema field.
- /bank (view), /deposit, /withdraw commands ('all' supported), with db_error
  handling; /balance shows the vault when non-zero.
- Coins leaderboard and /status money-supply now count net worth
  (balance + bank_balance), so banking never hides you from the board or the
  supply metric.
- Season reset wipes bank_balance too (no cross-season wealth hiding).

10 tests: deposit/withdraw math, guards, coin conservation, rob cannot touch the
vault, and net-worth accounting on the leaderboard + stats.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013VbAVsrZuYesea99mPMmPT

tests/test_bank.py

@@ -0,0 +1,86 @@
+"""Tests for the bank vault: rob-proof storage and net-worth accounting."""
+
+from core import economy
+
+from conftest import run
+
+UID = 6161
+ROBBER = 6162
+
+
+def _fund(fake_pb, uid: int, balance: int, bank: int = 0) -> None:
+    run(economy.get_user(uid))
+    rec = fake_pb.record_for(uid)
+    rec["balance"] = balance
+    rec["bank_balance"] = bank
+
+
+class TestDepositWithdraw:
+    def test_deposit_moves_liquid_to_bank(self, fake_pb):
+        _fund(fake_pb, UID, 1000)
+        res = run(economy.do_deposit(UID, 400))
+        assert res["ok"] and res["balance"] == 600 and res["bank"] == 400
+        rec = fake_pb.record_for(UID)
+        assert rec["balance"] == 600 and rec["bank_balance"] == 400
+
+    def test_withdraw_moves_bank_to_liquid(self, fake_pb):
+        _fund(fake_pb, UID, 100, bank=500)
+        res = run(economy.do_withdraw(UID, 300))
+        assert res["ok"] and res["balance"] == 400 and res["bank"] == 200
+
+    def test_deposit_more_than_liquid_rejected(self, fake_pb):
+        _fund(fake_pb, UID, 100)
+        res = run(economy.do_deposit(UID, 500))
+        assert not res["ok"] and res["reason"] == "insufficient"
+        assert fake_pb.record_for(UID)["balance"] == 100  # unchanged
+
+    def test_withdraw_more_than_bank_rejected(self, fake_pb):
+        _fund(fake_pb, UID, 0, bank=100)
+        res = run(economy.do_withdraw(UID, 500))
+        assert not res["ok"] and res["reason"] == "insufficient"
+        assert fake_pb.record_for(UID)["bank_balance"] == 100
+
+    def test_nonpositive_rejected(self, fake_pb):
+        _fund(fake_pb, UID, 1000, bank=1000)
+        assert run(economy.do_deposit(UID, 0))["reason"] == "invalid"
+        assert run(economy.do_withdraw(UID, -5))["reason"] == "invalid"
+
+    def test_banned_rejected(self, fake_pb):
+        _fund(fake_pb, UID, 1000)
+        fake_pb.record_for(UID)["eco_banned"] = True
+        assert run(economy.do_deposit(UID, 100))["reason"] == "banned"
+
+    def test_round_trip_conserves_coins(self, fake_pb):
+        _fund(fake_pb, UID, 1000)
+        run(economy.do_deposit(UID, 700))
+        run(economy.do_withdraw(UID, 700))
+        rec = fake_pb.record_for(UID)
+        assert rec["balance"] == 1000 and rec["bank_balance"] == 0
+
+
+class TestRobProof:
+    def test_rob_cannot_touch_banked_coins(self, fake_pb, monkeypatch):
+        # Target keeps everything banked, only a little liquid (< rob threshold).
+        _fund(fake_pb, UID, 50, bank=100_000)
+        _fund(fake_pb, ROBBER, 1000)
+        # Target has < 100 liquid, so a rob is rejected as "broke" - the vault is
+        # invisible to /rob (which only reads balance).
+        res = run(economy.do_rob(ROBBER, UID))
+        assert not res["ok"] and res["reason"] == "broke"
+        assert fake_pb.record_for(UID)["bank_balance"] == 100_000  # untouched
+
+
+class TestNetWorth:
+    def test_leaderboard_counts_bank(self, fake_pb):
+        _fund(fake_pb, UID, 100, bank=900)       # net worth 1000
+        _fund(fake_pb, ROBBER, 500, bank=0)      # net worth 500
+        board = dict((uid, worth) for uid, worth in run(economy.get_leaderboard(top_n=None)))
+        assert board[str(UID)] == 1000
+        assert board[str(ROBBER)] == 500
+
+    def test_economy_stats_counts_bank(self, fake_pb, monkeypatch):
+        monkeypatch.setattr(economy.house, "HOUSE_ID", None)
+        _fund(fake_pb, UID, 100, bank=900)
+        stats = run(economy.get_economy_stats())
+        assert stats["total_coins"] == 1000
+        assert stats["player_coins"] == 1000