Add entry point management to prime env push

[AmeenP]

Summary

This PR adds automatic entry point management to the prime env push command, enabling proper namespace-aware environment loading via Python entry points.

Changes

Prime CLI

• New flags:

  • --add-entry-point: Automatically add missing [project.entry-points.verifiers] entry
  • --entry-point-target MODULE[:ATTR]: Specify custom target (default: load_environment)

• Entry point enforcement:

  • Resolves environment early to determine owner/name for entry point key
  • Enforces exactly ONE entry point matching "owner/name" = "module:load_environment"
  • Auto-guesses target from project structure (checks for matching package dir or module file)
  • Provides clear error messages for multiple/mismatched entry points

Testing

• ✓ Correct single entry point validation
• ✓ Multiple entry points rejected with clear error
• ✓ Wrong entry point rejected with clear error
• ✓ Auto-add works when entry point missing
• ✓ Error shown when entry point missing and no auto-add
• ✓ Explicit targets work (with and without colon)
• ✓ Entry point guessing logic works correctly

Example Usage

# Auto-add entry point and push
cd /path/to/my-env
prime env push --add-entry-point

# Specify custom target
prime env push --add-entry-point --entry-point-target my_module:custom_loader

# Without auto-add (will error if missing)
prime env push  # Error with helpful message

Related

Companion PR for verifiers repo with entry point loading support coming next.