Documents agents-init/agents-vault's concept, purpose, and complete
behavior as its own manual section (16), separate from the auto-generated
function reference: the AGENTS.md convention and CLAUDE.md retirement,
the AGENTS/ sub-repository (layout, versioning, hooks), per-directory
discovery and its four-state normalization, the two safety mechanisms
(discovery containment, deliberately-tracked-file protection), the
plans/specs/devlogs wiring, and the launch lifecycle.
Inserted before Attribution/License (now 17/18) rather than mid-document,
since that's the only placement that doesn't touch any of the manual's
prose cross-references to other section numbers. docs/fish-config.index
updated to match (new keywords, renumbered attribution/license entries;
agents-init and agy were already indexed to their own function-reference
entries and are left pointing there, not redirected to this new page).
