Adds a visible control to change the devRoot directory from both the
project selection gate and the slide-out projects panel, so users no
longer need to hand-edit ~/.gsd/web-preferences.json.
- New /api/switch-root POST endpoint: validates path (exists, is dir),
persists to web-preferences.json (clearing lastActiveProject), and
returns discovered projects under the new root
- ProjectSelectionGate: shows current devRoot with "Change" link above
the project list; also shows "Change project root" link when no
projects are found under the current root
- ProjectsPanel: shows "Change" link next to the devRoot path in the
slide-out header
- Both views use the existing FolderPickerDialog for directory browsing
- 17 tests covering path validation, preference persistence, tilde
expansion, and end-to-end switch scenarios
Fixes#2264
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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