Adds a top-level layout_defaults setting that defines default
layout_options and layout_options_rules per layout. Workspaces without
their own layout_options or layout_options_rules automatically inherit
the global defaults. If a workspace defines either setting, all global
defaults for that layout are fully replaced.
Adds layout_options_rules to workspace configuration, allowing
layout_options to dynamically change based on container count. Uses the
same threshold semantics as layout_rules: when container count >=
threshold, the highest matching rule fully replaces the base
layout_options.