Add root README.md

[itdoadmin]

I've added a README.md file to the project root that outlines the project's overview, structure, technology stack, and links to key documents. The goal is to make it easier for new participants to grasp the overall picture of the project.

[Copilot]

Pull Request Overview

Adds a top-level README and aligns various subproject docs to reflect updated setup steps, directory layout, and schema details.

• Introduce root README.md with project overview, tech stack, and structure
• Update subproject getting-started guides (EN/JA) and developer guide for Python 3.13+, .venv, install commands, and startup ports
• Expand roadmap and API reference docs with detailed subtasks, schema definitions, and authentication notes

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	New root README with high-level overview, tech stack, and repo structure
flet-multiplatform-app/docs/getting_started.md	Updated prerequisites, venv naming, install commands, and launch steps
flet-multiplatform-app/docs/GETTING_STARTED_JA.md	Synced Japanese guide with new version, venv, install, and startup
flet-multiplatform-app/docs/development_roadmap.md	Expanded test-coverage and documentation roadmap with current status and subtasks
flet-multiplatform-app/docs/api_reference.md	Added schema definitions, refined auth notes, and endpoint examples
flet-multiplatform-app/docs/DEVELOPER_GUIDE.md	Revised setup/install commands, project structure, and launch instructions
flet-multiplatform-app/README.md	Refreshed app-level README to match updated layout and docs references

Comments suppressed due to low confidence (1)

flet-multiplatform-app/docs/api_reference.md:7

• The base URL note mentions ports may change but examples later still assume 8000. Consider defining a single variable (e.g. API_PORT) or consistently using 8001 across examples to avoid confusion.

**ベースURL**: `http://localhost:8000/api/v1` (ポートは設定により`8001`等に変更される場合があります)

[Copilot]

The root README references a tools/ directory, but the repository doesn’t include it. Either add that directory or update the README to reflect the actual structure.

Suggested change

	- `tools/`:
	開発効率を向上させるための各種スクリプトや補助ツール群が格納されています。詳細は `tools/README.md` を参照してください。
	<!-- The `tools/` directory reference has been removed as it is not part of the repository. -->

[Copilot]

Switching from pip install -r requirements.txt to pip install . may confuse users since requirements.txt still exists. Clarify when to use each command or document the replacement of the requirements file.

Suggested change

```

このコマンドは、プロジェクトの pyproject.toml または setup.py ファイルに記載された依存関係をインストールします。

注意: このプロジェクトでは requirements.txt ファイルは使用していません。すべての依存関係は pyproject.toml または setup.py に記載されています。従来の pip install -r requirements.txt は不要です。

[Copilot]

[nitpick] Installing editable extras often requires quoting (e.g. pip install -e " .[dev]") to avoid shell interpretation issues. Consider adding the quotes for cross-shell compatibility.

Suggested change

	pip install -e .[dev]
	pip install -e ".[dev]"