bridgev2/legacymigrate: add post-migrate hook

[sumnerevans]

Signed-off-by: Sumner Evans [email protected]

[Copilot]

Pull Request Overview

This PR adds a post-migrate hook to process each legacy portal during migration.

• Added a new function field, PostMigratePortal, in BridgeMain to handle per-portal migration actions.
• Updated the migration process to call the PostMigratePortal hook and handle errors accordingly.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
bridgev2/matrix/mxmain/main.go	Added a new function field for the portal migration hook.
bridgev2/matrix/mxmain/legacymigrate.go	Integrated the PostMigratePortal hook call in the migration process.

Comments suppressed due to low confidence (1)

bridgev2/matrix/mxmain/legacymigrate.go:242

• [nitpick] Consider adding test coverage for the scenario where PostMigratePortal returns an error to ensure proper error handling.

if br.PostMigratePortal != nil {