fix(migration): enhance migration logic to handle existing tables and…

[AxiosLeo]

… prevent duplicate migrations

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Note

Medium Risk
Changes migration execution control flow based on persisted state; incorrect detection or partial state could cause expected migrations to be skipped or rolled back unexpectedly.

Overview
Migration initialization now imports TransactionHandler from ./transaction and, when the migration tracking table already exists, loads existing rows into context.items instead of exiting blindly.

run() uses context.items to skip up migrations that have already been recorded and to skip down migrations that were never applied, reducing duplicate/invalid migration executions and adding clearer console output when the migration table is already present.

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