V2.1: Plafond negatif, reserve vault, carte bancaire visuelle, panel rewrite

- db: added client_negative_floor column to banks
- bank_manager: vault check on depot, negative floor on retrait/virement
- banque: new /banque set-plafond and /banque set-reserve commands
- bank_card: new Pillow-based bank card image generator
- panel: full rewrite (no more JSON), guild name in title, new banking flow

utils/db.py

@@ -12,6 +12,7 @@ CREATE TABLE IF NOT EXISTS banks (
     establishment_code INTEGER NOT NULL,
     vault_balance REAL DEFAULT 0.0,
     clients_total_balance REAL DEFAULT 0.0,
+    client_negative_floor REAL DEFAULT 0.0,
     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
     UNIQUE(guild_id, name),
     UNIQUE(guild_id, establishment_code)