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>

templates/snowflake/{{ cookiecutter.project_name }}/03-Characters/main_characters/01_protagonist.md

@@ -0,0 +1,13 @@
+# Name
+
+### Slug
+
+Age:
+
+Description:
+
+Motivation:
+
+Single Quote: 
+
+### Summary:

templates/snowflake/{{ cookiecutter.project_name }}/03-Characters/main_characters/02_antagonist.md

@@ -0,0 +1,13 @@
+# Name
+
+### Slug
+
+Age:
+
+Description:
+
+Motivation:
+
+Single Quote:
+
+### Summary: