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 }}/04-Outline/scene_breakdown/act_01.md

@@ -0,0 +1,11 @@
+## Act I – Setup (≈ 25 % of the story)
+
+<!-- Opening Image / Hook: A vivid snapshot of the protagonist’s ordinary world. Sets tone, setting, and the status‑quo the hero will soon leave. -->
+
+<!-- Inciting Incident: An event that disrupts the status‑quo and forces the protagonist to confront a problem. Creates the central conflict and gives the hero a reason to act. -->
+
+<!-- Key Event / Call to Adventure: The protagonist becomes aware of the stakes and is presented with a clear choice or challenge. Pushes the hero toward the journey; the point of no return begins to form. -->
+
+<!-- Debate / Refusal of the Call: The hero hesitates, doubts, or resists the upcoming change.  Highlights internal conflict and makes the eventual commitment feel earned. | -->
+
+<!-- Lock‑In / End of Act I: The hero decides to take action (or is forced into it). The story’s direction is now set. Marks the transition into the main confrontation; the protagonist is now “in the game.” -->