[SPIKE] Pipeline XML to JavaScript controller converter

[clavery]

Summary

Adds a new pipeline convert command that converts legacy B2C Commerce pipeline XML files to modern JavaScript controller code.

Features

• Full pipeline parsing: Parses pipeline XML into an intermediate representation (IR)
• Control flow analysis: Analyzes decision nodes, loops, and branching to generate proper if/else and for loops
• 60+ pipelet mappings: Converts common pipelets to their Script API equivalents:
  • Form pipelets (ClearFormElement, UpdateFormWithObject, etc.)
  • Product/Catalog pipelets (GetProduct, GetCategory, Search, etc.)
  • Customer pipelets (GetCustomer, LoginCustomer, CreateCustomer, etc.)
  • Basket/Order pipelets (GetBasket, AddProductToBasket, CreateOrder, etc.)
  • And many more...
• Unknown pipelet handling: Generates TODO comments for unmapped pipelets
• Unsupported pipelet handling: --allow-unsupported flag to continue conversion with warnings instead of failing
• Batch conversion: Glob pattern support for converting multiple pipelines at once
• Dry-run mode: Preview generated code without writing files

Usage

# Convert a single pipeline
b2c pipeline convert Account.xml --output ./controllers

# Convert multiple pipelines
b2c pipeline convert "pipelines/*.xml" --output ./controllers

# Preview without writing
b2c pipeline convert Cart.xml --dry-run

# Allow unsupported pipelets (generates TODO comments)
b2c pipeline convert Wishlist.xml --allow-unsupported

Test plan

• Convert sample pipeline XML files
• Verify generated code compiles and runs
• Test batch conversion with glob patterns
• Test --dry-run mode
• Test --allow-unsupported with pipelines containing unsupported pipelets
• Run test suite: pnpm run test