overrides-tricks conflated two distinct C3 concerns under one shared site
(overrides/environment), so __fish_config_op_overrides_key_bindings off
left tricks.fish's bang-bang bindings active while abbr.fish/puffer.fish/
config.fish's equivalent sites correctly disabled -- a half-dismantled
bang-bang system per docs/manual's own atomic-gating claim. Split into
tricks-manpager (overrides/environment, matches PAGER/EDITOR/CDPATH) and
tricks-bang (overrides/key-bindings, matches abbr.fish/puffer.fish/
config.fish's bang-related sites, per
docs/manual/08-components-reference/03-c3-key-and-environment-overrides.md).
Also fixes stale prose in config.fish's top-of-file comment: the guard
signature is now <identity> [<site>], not <category>.