Clarify UX for auto-detected ERC4626 vaults when the mint path is blocked

[starksama]

Summary

Users trying to loop the sUSDF/USDF market can hit an opaque estimateGas failure because the UI auto-detects the vault as ERC4626 and defaults to ERC4626 mode, even when that flow is effectively unusable for this vault.

In practice, users need to switch to swap mode manually, but the current UI does not make that obvious.

User impact

• User sees a raw estimateGas / custom error revert instead of actionable guidance
• UI appears broken even though another valid path exists
• This is especially confusing for auto-detected 4626 vaults that are permissioned / blocked / otherwise not mintable through the expected ERC4626 flow

Example report

• Market: https://www.monarchlend.xyz/market/1/0xe8c9d076ee7e6fcadd34165c44c08fe61533e7ab4accbed76d7e7f7d5a011708
• Wallet: 0x8467241838Bc761D9Ef4F8ae6790Ede292fbA2F9
• Symptom: transaction fails during gas estimation with an unknown custom error while trying to loop sUSDF/USDF

Suspected cause

The frontend auto-selects ERC4626 mode after detecting the vault standard, but this particular asset appears to require using swap mode instead (for example because minting is restricted / whitelist-gated / otherwise blocked in the ERC4626 path).

Expected behavior

When Monarch detects an ERC4626 vault whose mint/deposit path is not actually usable, the UI should not silently default users into a failing route.

Proposed improvements

• Detect when the ERC4626 path is unavailable / reverting and avoid auto-selecting it
• Or show a clear inline warning / fallback message telling users to use swap mode
• Replace raw estimateGas errors with a human-readable explanation
• Consider disabling or annotating auto-detected 4626 vault modes when they are blocked in practice

Acceptance criteria

• Users no longer see an unexplained estimateGas error for this flow
• The interface makes it clear when swap mode is required
• Auto-detected vault modes do not look supported when they are not actually usable