rename tagline to "IDE for Claude Code CLI"

clide is an IDE for the Claude Code CLI. The previous tagline
"Flutter desktop IDE for Claude Code" overemphasized the host
toolkit (Flutter is implementation detail, immediately obvious to
contributors) and was ambiguous about whether the integration
target is the CLI specifically.

Updates the welcome subtitle (i18n catalog + widget test + view),
the project description in pubspec.yaml, README and CLAUDE.md, the
CLI banner, and the web manifest/index.

Co-Authored-By: Claude <noreply@anthropic.com>

lib/kernel/src/i18n/catalog/builtin.welcome_en_us.json

@@ -1,6 +1,6 @@
 {
   "title": { "translation": "clide" },
-  "subtitle": { "translation": "Flutter desktop IDE for Claude Code" },
+  "subtitle": { "translation": "IDE for Claude Code CLI" },
   "open-project": { "translation": "Open project" },
   "open-project.hint": { "translation": "Pick a git repository to open as the workspace" },
   "tab.title": { "translation": "Welcome" }