Fix incorrect transaction cost display for USDC.e deposits without POL gas

## Description

When depositing USDC.e on Polygon without having POL for gas, the success toast incorrectly shows the total cost of the transaction (deposit + gas) as the deposit amount, rather than just the deposit amount.

## Root Cause Analysis

When the deposit succeeds, the data received from MM Pay has incomplete fee information:

```json
{
"bridgeFeeFiat": "0",
"chainId": "0x89",
"isPostQuote": undefined,
"networkFeeFiat": "0",
"targetFiat": "0",
"tokenAddress": "0x2791Bca1f2de4661ED88A30C99A7a9449Aa84174",
"totalFiat": "0.824763"
}
```

**Current Calculation Logic**
The current implementation calculates the deposit amount via:
```
totalFiat - bridgeFeeFiat - networkFeeFiat
```

However, for Polygon USDC.e deposits, the fees are set to `0` and `targetFiat` is also `0`, causing the full `totalFiat` (which includes gas costs) to be displayed as the deposit amount.

**Why This Happens**
When using Polygon USDC.e, a quote is not needed from the bridge service, so the fee breakdown data isn't populated. This creates a gap where the transaction succeeds but the confirmation UI doesn't have the correct data to display the actual deposit amount.

## Expected Behavior

The success toast should display only the deposit amount, excluding any gas fees.

## Actual Behavior

The success toast displays the total transaction cost (deposit + gas) as if it were the deposit amount.

## Steps to Reproduce

1. Have a wallet with USDC.e on Polygon but no POL for gas
2. Initiate a USDC.e deposit
3. Complete the transaction (gas paid via alternative method)
4. Observe the success toast showing incorrect deposit amount

## Related

- Jira: PRED-672
- This issue was identified as a gap that needs investigation when no quote is required for the transaction

## Technical Notes

The fix likely needs to handle the case where fee data isn't populated from the quote service, either by:
1. Populating the fee breakdown data even when a quote isn't needed
2. Calculating the deposit amount differently when fee data is unavailable
3. Using an alternative data source for the actual deposit amount