Migrated all 80 app JSON files to place config_path inside each
install_methods object instead of at the root level. This allows
different install methods (e.g. Debian vs Alpine) to have distinct
config paths.
Also updated AGENTS.md JSON structure example to reflect the change.
Move AI contribution guidelines from docs/AI.md to repo root AGENTS.md
following the open AGENTS.md standard (https://agents.md).
Most AI coding agents (Copilot, Codex, Cursor, etc.) automatically
discover and use AGENTS.md at the repo root.