Improve Developer Experience and Documentation

**Goal**: Enhance developer onboarding and daily workflow through improved docs and editor settings.

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### Tasks
- Write a comprehensive DEVELOPMENT.md (setup, structure, troubleshooting)
- Add VSCode workspace settings (`.vscode/settings.json` and `.vscode/extensions.json`)
- Document PocketBase schema in `docs/SCHEMA.md`
- Add troubleshooting guide `docs/TROUBLESHOOTING.md`
- Upgrade main README with badges, quick start, diagram, guidelines, demo credentials

**References:** See [QUICK_WINS.md](https://github.com/adhit-r/aran/blob/main/QUICK_WINS.md)

**Acceptance Criteria**
- New contributors can onboard and run the project with docs alone
- Recommended extensions/settings enforced for VSCode
- Schema and troubleshooting docs committed
- README clearly covers setup, usage, contribution, and project highlights

先閱讀 QUICK_WINS.md、現有的 README，以及儲存庫目前的文件和編輯器設定。更新或新增 DEVELOPMENT.md、.vscode/settings.json、.vscode/extensions.json、docs/SCHEMA.md 和 docs/TROUBLESHOOTING.md，然後確認 README 和新手導覽流程符合列出的驗收標準。

由索引模型根據 Issue 內容生成。