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.lock

@@ -1854,6 +1854,7 @@ dependencies = [
  "dirs",
  "eframe",
  "egui",
+ "minijinja",
  "pulldown-cmark",
  "rfd",
  "serde",
@@ -1878,6 +1879,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "memo-map"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5449c8c750f1a07ea702bbd212bd999fceece9b3d1508b17023b3e174583124b"
+
 [[package]]
 name = "memoffset"
 version = "0.9.1"
@@ -1902,6 +1909,16 @@ dependencies = [
  "paste",
 ]
 
+[[package]]
+name = "minijinja"
+version = "2.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86886cf6dbf4e614b19c9a1eec9775f021869d7eadde0fc73921a81b90c9b4c9"
+dependencies = [
+ "memo-map",
+ "serde",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.9"