release 2.2.0

Cut 2.2.0 from Unreleased — a large feature batch since 2.1.0 (collapser
cards, clide:// deep links, .editorconfig, the Phosphor-by-name icon
system, settings-modal wireframe, theme persistence, and a stack of UI
fixes). Bump pubspec to 2.2.0; trim three changelog bullets under the
60-word cap.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pubspec.yaml

@@ -13,7 +13,7 @@ description: >-
   subsystem handlers (pane, files, editor, git, pql), and the
   extension framework.
 publish_to: none
-version: 2.1.0
+version: 2.2.0
 repository: https://github.com/postmeridiem/clide
 # Short user-facing tagline (the welcome subtitle, web meta
 # description, etc.). Baked into lib/src/build_info.g.dart by