Migrate Account components to MUI v7



### 5. **Refactor `Account/` components for MUI v7**

**Why:**
Account flows often use forms, inputs, validation, and alerts — all MUI-heavy.

**Scope:**

* Fix TextField, Select, FormControl, Button usage
* Ensure error handling & helperText still render properly

**Suggested title:**
**Migrate Account components to MUI v7**

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