AssetManager 0.5.5.42

Repository documentation cleanup

Simplified the public README to released functionality, installation, operation, security, privacy, dependencies, updating, contribution information, and licensing.
Removed proposal-style architecture documentation from the public documentation tree.
Removed historical rollback and tentative implementation notes from public release notes.
Added Git ignore rules for maintainer-only development context and AI/chat handover files.
Updated the public-source exporter and release checker so maintainer-only files cannot be included in public source archives.
No application runtime logic, database schema, or user configuration was changed.