Migrate stacks/app_pipeline.go from survey to huh

[blsmth]

Summary

Migrate app/pipeline stack prompts in stacks/app_pipeline.go from survey to huh. This is the most complex migration file.

Details

• Complexity: High
• Prompts: 16 prompts (6 Selects, 4 Inputs, 2 Multilines, 1 Confirm, plus sub-methods)
• Includes AskForDatabase, AskForRedis, AskForSES sub-flows with conditional chaining
• Has databaseSelectTransform and redisSelectTransform
• One direct survey.AskOne call for data loss confirmation
• Split into multiple extracted form builders

Dependencies

• Requires AskForCluster (stacks/stacks.go), Redis (stacks/redis.go), and Database (stacks/database.go) migrations to be completed first

Checklist

• Extract multiple form builder functions (pure, no AWS mocks needed)
• Replace all ui.AskQuestions and survey.AskOne calls with huh forms
• Replace transform functions with typed huh.NewOption calls
• Handle conditional sub-flows (AskForDatabase, AskForRedis, AskForSES)
• Add teatest + ui/uitest tests for each sub-flow
• Add VHS recordings for visual verification
• Verify non-interactive mode still works