chore: initial project scaffold

Set up IdeaForge project structure with documentation, architecture spec,
and development guidelines for both backend (Python) and frontend (Flutter).

changelog.md

@@ -0,0 +1,14 @@
+# changelog
+
+All notable changes to IdeaForge.
+
+Format based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
+This project uses [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+- Initial project scaffold
+- Project documentation (readme, CLAUDE.md, changelog)
+- Backend and frontend directory structure