feat: Replace cookiecutter with built-in MiniJinja templating

- Add MiniJinja dependency for Jinja2-compatible templating
- Create new project_template.rs module for template rendering
- Bundle snowflake template in templates/snowflake/ directory
- Remove dependency on external cookiecutter Python tool
- Handle Gitea publishing natively in Rust instead of Python hooks
- Update default template path to use bundled template with fallback
- Update README to reflect new built-in templating
- All tests pass

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

Cargo.toml

@@ -21,6 +21,8 @@ ureq = { version = "2", default-features = false, features = ["tls"] }
 # Pure-Rust reader of Hunspell .aff/.dic dictionaries for offline spell
 # checking, so the binary stays self-contained (no C libhunspell to link).
 spellbook = "0.4.2"
+# Templating engine for project scaffolding (replaces cookiecutter dependency)
+minijinja = { version = "2", features = ["builtins", "loader"] }
 
 [profile.release]
 opt-level = 2