The KQL parser produced its own validation errors but imported them from the
search service's query package. Move them into pkg/kql and let the search
backend consume kql.IsValidationError, so the parser stops depending on a
service package.
both engines now agree on names, titles, tags, paths, types, sizes, dates,
hidden flags, facet values and wildcards. quotes only delimit phrases and
the equals operator matches the whole field value, following the kql spec.
the index name carries a generation so a changed mapping starts on a fresh
index, MIGRATION.md says how to fill it.
Four cases covering the distinct grammar paths touched by the
new Key rule: dotted key in a TextPropertyRestrictionNode,
multi-level key (stressing the Kleene part), dotted key in a
GroupNode (the k:Key? branch), and a dot on the value side
that must stay a literal character.