Fix min_deposit/min_withdraw mismatch: 10 USDT backend vs 1 USDT wallet UI

wallet-android's Bridge screen has always advertised a 1 USDT minimum
(MIN_USDT constant), but usdt-bridge's actual min_deposit/min_withdraw
defaulted to 10 USDT since the tool's original scaffold commit - nobody had
ever reconciled the two. Confirmed live: a real user swap of ~1 USDT landed
correctly at the multisig custody address but was silently skipped by
listen_deposits (amount < min_deposit), so the user never received wUSDT
despite the wallet telling them 1 USDT was a valid amount.

Backend now matches the value already promised to users, not the other way
around - changing the wallet's displayed minimum after users have already
relied on it would be the wrong direction to reconcile this in.

tools/usdt-bridge/bridge_config.json

@@ -3,8 +3,8 @@
   "pezkuwi_rpc": "wss://asset-hub-rpc.pezkuwichain.io",
   "polkadot_usdt_asset_id": 1984,
   "pezkuwi_wusdt_asset_id": 1000,
-  "min_deposit": 10000000,
-  "min_withdraw": 10000000,
+  "min_deposit": 1000000,
+  "min_withdraw": 1000000,
   "fee_basis_points": 10,
   "seed_path": "bridge_seed.json",
   "db_path": "bridge_db.json",

tools/usdt-bridge/src/main.rs

@@ -23,7 +23,9 @@
 //!   `Multisig.approveAsMulti`/`asMulti`, which is expected to happen through pwap-web's
 //!   existing multisig UI (shared/lib/multisig.ts, shared/lib/usdt.ts, MultisigMembers.tsx),
 //!   not this relayer.
-//! - Minimum deposit/withdraw: 10 USDT
+//! - Minimum deposit/withdraw: 1 USDT (matches wallet-android's advertised minimum - this was a
+//!   leftover scaffold default of 10 USDT that nobody had reconciled with the app's own 1 USDT
+//!   minimum until a real user swap below 10 but above 1 USDT was silently skipped)
 //! - Fees: Configurable (default 0.1%)
 
 use anyhow::{anyhow, Context, Result};
@@ -152,8 +154,8 @@ impl Default for BridgeConfig {
             pezkuwi_rpc: "wss://asset-hub-rpc.pezkuwichain.io".to_string(),
             polkadot_usdt_asset_id: 1984,
             pezkuwi_wusdt_asset_id: 1000,
-            min_deposit: 10_000_000,      // 10 USDT (6 decimals)
-            min_withdraw: 10_000_000,
+            min_deposit: 1_000_000,      // 1 USDT (6 decimals) - matches wallet-android's advertised minimum
+            min_withdraw: 1_000_000,
             fee_basis_points: 10,         // 0.1%
             seed_path: PathBuf::from("bridge_seed.json"),
             db_path: PathBuf::from("bridge_db.json"),