Fix five coherence bugs in profile switching:
1. Model picker ignored profile default (localStorage stale key)
2. Workspace list was global (not profile-scoped)
3. DEFAULT_WORKSPACE was a boot-time singleton
4. Session list showed all profiles (no filtering)
5. switchToProfile() didn't refresh workspaces or sessions
Backend: workspace storage is now profile-local for named profiles,
switch_profile() returns default_model and default_workspace.
Frontend: switchToProfile() clears stale model pref, refreshes
workspace list and session list, sessions.js filters by active profile
with 'Show N from other profiles' toggle.
8 new tests. 400 pass / 23 fail (identical to baseline).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
3520fa5643