Add cmake.languageServerOnlyMode setting for language services without project integration

[Omotola]

Summary

Adds a new cmake.languageServerOnlyMode setting that enables CMake language services (hover, completion) while disabling all project integration (kit selection, configure, build, test). This is useful for users who want CMake language support but don't have CMake installed locally.

Related Issue

Closes #4516

Changes

• Setting: Added cmake.languageServerOnlyMode (boolean, defaults to false, machine scope)
• Config: Updated src/config.ts with new setting, getter, and EventEmitter
• Extension lifecycle: Early return in postWorkspaceOpen() to skip kit scanning and configure-on-open
• Project integration: Suppressed save-triggered reconfigure, bad-executable toasts, and driver initialization when enabled
• UI: Gates cmake:enableFullFeatureSet context key to hide build/test/kit commands and views
• Documentation: Added setting to cmake-settings.md and CHANGELOG

Testing

Tested Locally, confirmed that with the new setting on and a fake cmake path, there's no auto-configure when saving cmakefiles, and during manual configure output shows a message indicating language server only mode is enabled.

Notes

• The language services implementation was already fully decoupled from the CMake executable, so no changes to language service code were needed
• The setting requires manual user configuration; it does not auto-detect missing CMake