Refactor main parsing flow and add regression coverage

[jwilder]

What changed

• Refactored main to move argument parsing and related setup into smaller helper functions, reducing branching and complexity in the entrypoint.
• Added focused tests for:
  • delimiter parsing
  • wait URL parsing
  • HTTP header parsing
  • processing template file and directory arguments

Why

This fixes the high-complexity issue reported for main by separating parsing logic from the top-level flow. The change makes the code easier to follow and maintain, while adding regression coverage for parsing and template-processing behaviors that are now handled by dedicated helpers.

How to verify

• Run the test suite:
  • go test ./...
• Optionally review the new unit tests in main_test.go to confirm coverage for valid and invalid parsing cases.