craft-flags keeps one per-user file, ArtCraft/flags.toml beside the AI
layer's ArtCraft/ai, that the launcher and every app read; CRAFT_FLAGS
overrides it for one run. Every flag is off by default. The first two:
AI-MCP (AI agents through MCP) and AI-MODELS (AI models and services).
Loading never fails: a missing or damaged file means defaults, with the
reason in Flags::problems. set() changes one flag atomically and keeps
everything else in the file, and never overwrites a file it can't read.
In the browser every flag is at its default.
Closes#1118
---------
Co-authored-by: David Mann <daaavid.mann@gmail.com>
