[Bug]: MetaMask `send` deeplink unusable on 7.81.2 — decimal chainId → "Network with chain ID 1 not found", hex/omitted chainId → no navigation

### Describe the bug

### Describe the bug
The `send` deeplink to Ethereum mainnet cannot be opened on MetaMask Mobile 7.81.2.
Ethereum Mainnet IS configured (Chain ID `0x1`, Infura RPC) and the account holds
ETH and USDC on mainnet, yet no chainId format routes to the Send screen:

| Deeplink chainId | Result |
|---|---|
| `@1` (decimal) | Error: "Network with Chain ID 1 not found in your wallet. Please add the network first." |
| `@0x1` (hex) | MetaMask opens but stays on the home screen, no navigation |
| omitted | MetaMask opens but stays on the home screen, no navigation |

Only the decimal form (the format shown in the official docs) is recognized as a
send, but its network lookup fails even though mainnet exists — consistent with the
hex/decimal network-key regression in #15127.

### Steps to reproduce
1. Have Ethereum Mainnet configured and funded (ETH + USDC on mainnet).
2. Tap any of these universal links on the device:
- `https://link.metamask.io/send/0xd05a432ad6bdfe5520addae7f27fc325de036d89@1`
- `https://link.metamask.io/send/0xd05a432ad6bdfe5520addae7f27fc325de036d89@0x1`
- `https://link.metamask.io/send/0xd05a432ad6bdfe5520addae7f27fc325de036d89`
3. Observe the results in the table above.

### Expected behavior
The deeplink opens the Send confirmation screen, prefilled with the recipient on
Ethereum mainnet (per https://docs.metamask.io/metamask-connect/evm/guides/metamask-exclusive/use-deeplinks/).

### Actual behavior
No chainId format works: decimal errors with "network not found"; hex and omitted
chainId open the app but never navigate to Send.

### Version
- MetaMask Mobile: **7.81.2**
- Platform / OS: **iOS 26.5**, device iPhone 16
- Opened via: tapping the `https://link.metamask.io/...` universal link (not QR scan)

### Additional context
- Ethereum Mainnet is present in Settings → Networks (Chain ID `0x1`, Infura mainnet RPC, ETH, etherscan) and the wallet holds mainnet assets, so the network is not actually missing.
- The same app and launch path successfully open other wallets via their deeplinks (e.g. Trust Wallet opens its Send flow correctly), so the issue is isolated to MetaMask's `send` deeplink handling, not our integration.
- Possibly related / same root cause: #8466, #11966, #15127.

### Expected behavior

The deeplink opens the Send confirmation screen, prefilled with the recipient on
Ethereum mainnet (per https://docs.metamask.io/metamask-connect/evm/guides/metamask-exclusive/use-deeplinks/).

### Screenshots/Recordings

_No response_

### Steps to reproduce

1. Have Ethereum Mainnet configured and funded (ETH + USDC on mainnet).
2. Tap any of these universal links on the device:
- `https://link.metamask.io/send/0xd05a432ad6bdfe5520addae7f27fc325de036d89@1`
- `https://link.metamask.io/send/0xd05a432ad6bdfe5520addae7f27fc325de036d89@0x1`
- `https://link.metamask.io/send/0xd05a432ad6bdfe5520addae7f27fc325de036d89`
3. Observe the results in the table above.

### Error messages or log output

```shell

```

### Where was this bug found?

Live version (from official store)

### Version

7.81.2

### Build number

5434

### Build type

None

### Device

iPhone 16 (iOS 26.5)

### Operating system

iOS

### Additional context

_No response_

### Severity

_No response_

Reproduce the three documented send universal links on MetaMask Mobile and trace the send deeplink entry point through chainId parsing and network lookup. Done means the decimal, hexadecimal, and omitted-chainId cases route to the Send confirmation screen with the recipient on Ethereum mainnet, without a false network-not-found error.

Written by the indexing model from the issue text.