feat(migration, builder): add changeColumn method for modifying exist…

[AxiosLeo]

…ing columns

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Note

Medium Risk
Adds a new migration operation that emits ALTER TABLE ... MODIFY COLUMN, which can alter live schema and potentially cause data/type incompatibilities if used incorrectly.

Overview
Adds a new migration API changeColumn(tableName, columnName, options) (and TypeScript typings) to modify existing table columns.

Implements SQL generation in ManageSQLBuilder.changeColumn to render ALTER TABLE �... MODIFY COLUMN using existing column rendering/validation, and wires it into migration so migrations enqueue the generated query.

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