Summary

• Adds templates edit <id> command to modify existing templates in-place
• Supports updating name (--name), description (-d), and exercises (-e) independently
• Adds updateTemplate() method to storage layer, following the existing updateExercise() pattern

Test plan

• Updates template name and description while preserving exercises
• Replaces template exercises while preserving other fields
• Throws error when editing non-existent template
• All 120 tests pass, validation clean

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