Revert fallback logic for WHERE clause validation

[Copilot]

Reverted confusing fallback logic that automatically promoted the first logical operation to the WHERE clause when none was explicitly set. This behavior was non-obvious and changed query semantics silently.

Changes

• QueryDelete.kt: Removed fallback logic, restored require(where != null) validation
• QuerySelect.kt: Removed fallback logic, restored require(where != null) validation

Both query builders now enforce explicit WHERE clause specification, making the API behavior clear and predictable.

// Before: First operation silently became WHERE clause
QueryDelete.builder(table)
    .and(field.eq("value"))  // This became WHERE, not AND
    .build()

// After: WHERE must be explicit
QueryDelete.builder(table)
    .where(field.eq("value"))  // Clear intent
    .build()

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