feat: refactor and optimize insight tree

[starboyate]

Summary

• refactor the insight tree pipeline to separate point operation resolution from application and tighten prompt/output contracts
• harden insight tree construction and retrieval with stable point identity, layered evidence normalization, and safer branch/root expansion behavior
• remove the unused confidence field from insight models, persistence mappings, and schema initialization paths
• align JDBC and MyBatis store schema contracts with the updated insight tree model and add regression coverage for fresh-install bootstrap behavior

Breaking Changes

• remove confidence from insight-related domain models and storage mappings
• downstream integrations that depend on insight confidence must migrate to the layered evidence model
• fresh-install schemas no longer create legacy insight confidence columns

Review Guide

• 1a67001 feat: optimize insight point operations pipeline
• b3dd86b feat: harden insight tree construction
• e00f57a feat: remove insight confidence and add layered evidence
• eb5dbd8 fix: harden insight tree expansion and schema contracts

Testing

• mvn -pl memind-core,memind-plugins/memind-plugin-jdbc,memind-plugins/memind-plugin-spring-boot-starters/memind-plugin-mybatis-plus-starter -am test