Clarify LabNote’s project-ledger positioning

[Wonderforge-Lab]

Phase 1: README opening

Clarifies LabNote’s first-screen category and search language without changing its workflow or claims.

• positions LabNote as a human-controlled, git-native project ledger;
• names the cross-session use case across AI assistants, coding agents and chats;
• surfaces selected sources, handoffs, reviews, decisions and next actions;
• states the human review boundary and the basic no-service/no-database/no-model-key constraint;
• aligns the Simplified Chinese README opening, as required by the repository’s locale-freshness validation.

Deliberately limited to the README opening in English and Simplified Chinese. Deeper documentation and GitHub metadata/topics remain later phases.