fix: Properly initialize ~/.aisbf/ directory with all config and prompt files

- Copy markdown prompt files (*.md) to ~/.aisbf/ on first run
- Fix installation location search order (user-local first, then system)
- Add JSON validation and proper error handling for all config files
- Fix invalid JSON syntax in default rotations.json
- Existing files are never overwritten
- Config files are properly copied from ~/.local/share/aisbf, /usr/local/share/aisbf, /usr/share/aisbf or source directory depending on installation type

config/rotations.json

 {
   "notifyerrors": false,
   "rotations": {
-    }
   }
 }