Stability & Open Source Release

Prepares ChatML for open source release with stability improvements, better error handling, and documentation updates.

Fixes

• Fixed null pointer crash in the File History panel when commits were missing
• Used credential cascade consistently for AI features in server handlers
• Prevented false-positive @mention pills from appearing in log and paste content
• Fixed resource leaks and improved error handling in the backend

Misc

• Rewrote README for open source release