Insert Row modal: ENUM fields should render as a dropdown, not a plain text input

## Problem
In the "Insert row" modal, `ENUM` column fields are rendered as plain text inputs. Users must type the exact enum value from memory with no guidance on valid options.

## Steps to reproduce
1. Run a query on a table that has an ENUM column (e.g., `customers.status` is `enum('active','inactive','suspended')`)
2. Click "+ New row"
3. The `status` field shows a plain text input with placeholder "default: active"

## Expected behaviour
ENUM fields should render as a `` dropdown pre-populated with all valid enum values. This:
- Prevents invalid input at the UI level
- Makes the valid options immediately discoverable
- Matches the UX of tools like TablePlus, Sequel Pro, DBeaver

## Note
The full enum definition IS available — it is already shown in the modal label (`enum('active','inactive','suspended')`), so the values can be parsed to build the dropdown.