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 }}/05-Plot/act_1/scene_01.md

@@ -0,0 +1,23 @@
+# Title
+
+# Slug
+
+## POV:
+
+## Characters:
+
+## Setting:
+
+## Conflict:
+
+## Feeling to convey:
+
+## Word Count Target:
+
+## The Setup:
+
+## The Reveal:
+
+### Things to Note:
+
+### Rough draft: