chore: remove internal planning and improvement notes (#39)

This is an open-source educational repository, not a commercial sales
target. The actual interview content (questions, answers, schemas, JSON
API exports, translations) stays intact. Just drop the internal
planning/improvement-tracking docs:

- CLAUDE.md
- IMPROVEMENTS.md (Arabic improvement plan)
- Firebase_Implementation_Plan.md
- DSA/IMPLEMENTATION_PLAN.md, Git/implementation-plan.md
- .claude/, .agent/ working state

The questions in Flutter/Basics/* that mention "Gemini, Claude" stay —
they are legitimate factual content for "How do you integrate AI
features into a Flutter app safely?" interview prep.

Author: mahmoodhamdi