feat: Align Text Memory Addition and Retrieval Logic across general_text/naive_text and tree_text

[starsalwaysineyes]

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

Inconsistent Ingestion: In core.add, general/naive backends write raw data directly, while tree_text uses mem_reader + scheduler.
Fragmented Search API: _search_with_engine uses try/except to handle mismatched search() signatures (e.g., the mode parameter), leading to messy branching logic.
Align Write Path: Use a unified extraction strategy (e.g., mem_reader) for all text backends.
Standardize Search: Unify search() arguments (like mode and info) to remove conditional call logic.

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

[github-actions]

This issue has been automatically marked as stale due to inactivity.