fix: template nesting

[rochecompaan]

This refactor makes template-starter reliably generate a nested Copier template
repo and cleans up the two-phase bootstrap flow.

1.Nested template output is now correct

• Starter renders a generated repo with:
  • root copier.yml, README.md, .github/workflows/template-correctness.yaml
  • inner template/ payload for second-stage rendering
• Deferred files (like inner answers file) are preserved with proper Jinja/raw handling.

2.Two-phase post-copy logic is explicit and maintainable

• Replaced shell orchestration with Python phase scripts:
  • template/.scaf/starter-post-copy.py.jinja (starter phase)
  • template/template/.scaf/post-copy.py.jinja (generated-template phase)
• copier.yml tasks now run these Python scripts directly.

3.Semantic-release dependency init behavior fixed

• If semantic-release is enabled, dependency install runs in both phases.
• Starter phase safely handles unresolved Jinja in dependency files before installing.
• Final template still uses its normal scripts/init-dev.sh flow.

4.Git bootstrap improvements

• Both phases now:
  • init git repo when missing
  • optionally configure/create remote
  • create an initial commit automatically when repo was newly initialized
• Initial commit uses template author/email and --no-verify to avoid hook bootstrap failures.