feat: Add recursive directory selection and enhance prompt builder

- Add `select_all` option to recursively add directory contents
- Implement `select_all_files_and_dirs` for file traversal
- Rework prompt building with file tree and content formatters
- Improve `get_file_extension` to handle dotfiles and special files
- Update prompt template to use new structured data model

lib/develop/heroprompt/templates/prompt.template

@@ -0,0 +1,11 @@
+<user_instructions>
+@{prompt.user_instructions}
+</user_instructions>
+
+<file_map>
+@{prompt.file_map}
+</file_map>
+
+<file_contents>
+@{prompt.file_contents}
+</file_contents>