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be spent, gambled or given until withdrawn - the deliberate trade-off against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

commands/economy_profile_commands.py

@@ -292,6 +292,9 @@ def register_economy_profile_commands(
             color=0xF4C430,
         )
         embed.add_field(name=S.BALANCE_UI["saldo"], value=coin(data["balance"]), inline=True)
+        bank_balance = data.get("bank_balance", 0)
+        if bank_balance:
+            embed.add_field(name=S.BANK_UI["f_bank"], value=coin(bank_balance), inline=True)
         streak = data.get("daily_streak", 0)
         if streak:
             embed.add_field(