test: add tests for migrate command

[ivanauth]

Description

Fixes #2758 by refactoring migrate execution for testability and adding coverage.

Changes

• Extract MigrateConfig
• Add executeMigrate helper
• Add migrate tests

[codecov]

Codecov Report

❌ Patch coverage is 92.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.04%. Comparing base (0b5d8c5) to head (1d3699c).
⚠️ Report is 57 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/cmd/migrate.go	92.50%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2822      +/-   ##
==========================================
- Coverage   78.46%   75.04%   -3.42%     
==========================================
  Files         459      484      +25     
  Lines       44674    58046   +13372     
==========================================
+ Hits        35048    43553    +8505     
- Misses       6769    11445    +4676     
- Partials     2857     3048     +191     

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