feat: Persistent, User-Scoped Memory Skill

[hijzy]

Pre-submission checklist | 提交前检查

• I have searched existing issues and this hasn't been mentioned before | 我已搜索现有问题，确认此问题尚未被提及
• I have read the project documentation and confirmed this issue doesn't already exist | 我已阅读项目文档并确认此问题尚未存在
• This issue is specific to MemOS and not a general software issue | 该问题是针对 MemOS 的，而不是一般软件问题

Problem Statement | 问题陈述

Why memory skill is needed

Many practical scenarios require a Skill to remember things over time:

User preferences (writing tone, coding style, language, expertise level)

Ongoing projects (documents, research topics, software features in progress)

Past decisions (chosen architecture, constraints, goals)

Learning or coaching progress

Without memory:

Users must constantly repeat context

Multi-step or long-term tasks become fragile

Skills cannot behave consistently or feel “collaborative”

This makes Skills feel like one-off functions rather than components in a longer workflow.

Willingness to Implement | 实现意愿

• I'm willing to implement this myself | 我愿意自己解决
• I would like someone else to implement this | 我希望其他人来解决