chore: fix materialized view recreate summary

[tianzhou]

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[Copilot]

Pull request overview

This PR fixes the summary display for materialized views that are recreated due to table dependencies. Previously, such views were incorrectly counted as "adds" when they should be counted as "modifications" since the view existed before and is being recreated.

• Introduces a new DiffOperationRecreate operation to distinguish DROP operations that are part of a DROP+CREATE cycle
• Updates plan summary logic to treat recreate operations as modifications rather than additions
• Ensures consistent display across both the plan summary counts and the detailed change list

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
testdata/diff/dependency/table_to_materialized_view/plan.txt	Test data showing expected output where recreated materialized view is now correctly shown as "2 to modify" instead of "1 to add, 1 to modify"
internal/diff/diff.go	Adds DiffOperationRecreate enum value and uses it in generatePreDropMaterializedViewsSQL to mark views that will be recreated
internal/plan/plan.go	Updates summary calculation and display logic to track recreate operations and convert subsequent create operations to modifications

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