docs: multilingual readme

[sairin1202]

No description provided.

[Copilot]

Pull request overview

This PR updates the project branding and documentation across multiple language README files, changing "MemU" to "memU" (lowercase 'M') and revising the core messaging to emphasize 24/7 proactive agents with reduced LLM token costs.

Changes:

• Rebranded project name from "MemU" to "memU" across all documentation files
• Updated product positioning to focus on cost efficiency and user intent capture instead of continuous learning features
• Revised use case examples from contextual assistance to information recommendation, email management, and financial monitoring

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
readme/README_zh.md	Chinese documentation updated with new branding and revised feature descriptions
readme/README_ko.md	Korean documentation updated with new branding and revised feature descriptions
readme/README_ja.md	Japanese documentation updated with new branding and revised feature descriptions
readme/README_fr.md	French documentation updated with new branding and revised feature descriptions
readme/README_es.md	Spanish documentation updated with new branding and revised feature descriptions
readme/README_en.md	English documentation updated with new branding and revised feature descriptions
README.md	Main README updated with lowercase "memU" branding

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Inconsistent section heading change from 'Core Capabilities' to 'Core Features'. The Chinese, Korean, Japanese, French, and Spanish versions use translations equivalent to 'Core Features/Capabilities', but this change in the English version may indicate an intentional shift. Verify this is the intended heading across all language versions for consistency.

Suggested change

	## ✨ Core Features
	## ✨ Core Capabilities