fix(web): correct asset IDs/decimals + chain routing, string-BigInt amounts, presale signer

Fund-logic hardening (audit remediation):
- TransferModal: source asset id/decimals from the canonical MINTABLE_ASSETS
  (wUSDT=1000, wDOT=1001, wETH=1002, wBTC=1003) instead of the wrong hardcoded
  ids (BTC=3 was the deprecated "Old USDT", ETH=4, DOT=5). Route every non-native
  asset through the Asset Hub api; only native HEZ uses the relay balances pallet.
  Removes the latent wrong-asset / wrong-chain transfer.
- Replace BigInt(parseFloat(x)*10**dec) with string-based parseTokenInput in
  TransferModal + 3 DEX init modals; BigInt(float) threw RangeError on common
  fractional amounts (e.g. 100.3 HEZ), breaking sends and pool/bridge init.
- Presale.contribute now resolves a signer via getSigner and passes { signer }
  to signAndSend (was signer-less -> broken for all users).
- presale.ts contribute/refund/claimVested now reject on dropped/invalid/usurped/
  retracted tx states instead of hanging the UI forever.

shared/lib/presale.ts

@@ -445,6 +445,10 @@ export async function contribute(
           if (status.isInBlock) {
             onStatus?.('Transaction in block...');
           }
+          if (status.isDropped || status.isInvalid || status.isUsurped || status.isRetracted) {
+            resolve({ success: false, error: 'Transaction was dropped or invalidated by the network. Please try again.' });
+            return;
+          }
           if (status.isFinalized) {
             if (dispatchError) {
               let errorMessage = 'Transaction failed';
@@ -489,6 +493,10 @@ export async function refund(
           if (status.isInBlock) {
             onStatus?.('Refund in block...');
           }
+          if (status.isDropped || status.isInvalid || status.isUsurped || status.isRetracted) {
+            resolve({ success: false, error: 'Refund was dropped or invalidated by the network. Please try again.' });
+            return;
+          }
           if (status.isFinalized) {
             if (dispatchError) {
               let errorMessage = 'Refund failed';
@@ -533,6 +541,10 @@ export async function claimVested(
           if (status.isInBlock) {
             onStatus?.('Claim in block...');
           }
+          if (status.isDropped || status.isInvalid || status.isUsurped || status.isRetracted) {
+            resolve({ success: false, error: 'Claim was dropped or invalidated by the network. Please try again.' });
+            return;
+          }
           if (status.isFinalized) {
             if (dispatchError) {
               let errorMessage = 'Claim failed';