refactor(editor): scope query completion by database

[J2TeamNNL]

Summary

• Wave 1 foundation only for query completion by database.
• No SingleStore/profile catalogs/uppercase/docs product changes yet.

Architecture / ABI

• PluginKit change is source-reviewed additive: new non-frozen types and a defaulted protocol requirement, no version bump yet; ABI gate still required in CI/Xcode.

Test plan / results

• git diff --check passed
• swift frontend parse passed for all changed Swift files
• targeted Xcode tests, AllPlugins build, PluginKit ABI build gate, swiftlint strict remain unchecked because active developer directory is CommandLineTools and SourceKit cannot load
• No generated xcodeproj/build artifacts

Follow-up

• Complete the remaining Xcode validation gates once Xcode is available.