openwiki init overwrites existing AGENTS.md and CLAUDE.md without warning

[wupengbo125]

Problem

Running openwiki init overwrites the project's existing AGENTS.md and CLAUDE.md files, destroying all user content silently.

These files often contain project-specific agent rules, skill configurations, and development guidelines that users have carefully maintained.

Expected Behavior

openwiki init should append the OpenWiki block (between <- If AGENTS.mdorCLAUDE.mdalready exists,openwiki init should OPENWIKI:START --> and <- If AGENTS.mdorCLAUDE.mdalready exists,openwiki init should OPENWIKI:END --> markers) to existing AGENTS.md / CLAUDE.md files, preserving all original content.

Actual Behavior

openwiki init silently replaces the entire content of AGENTS.md and CLAUDE.md with OpenWiki's boilerplate.

Steps to Reproduce

1. Have a project with an existing AGENTS.md or CLAUDE.md containing custom content.
2. Run openwiki init.
3. Original file content is completely replaced.