feat(workspaces): workspace switcher, invite dialog, and Settings sub-tabs

[gabrielste1n]

Summary

Desktop UI for the Workspaces, Teams, Shared Collaboration, and Developer API feature (paired with OpenWhispr/openwhispr-api#62).

• Workspace switcher at the top of the sidebar (compact selector + menu)
• "Invite teammate" / "Create workspace" button above Settings (conditional copy based on whether the user has any workspaces)
• Settings → Workspace section with 5 sub-tabs: General, Members, Teams, Billing, Developer
• Deep-link invitation handler — openwhispr://invitations/<token> opens AcceptInvitationModal (routes through onboarding sign-in if signed out, then resumes)
• One-time API key reveal modal (developer sub-tab); workspace keys use ow_wks_live_... prefix
• New i18n keys across all 10 locales (settingsPage.workspace.*, sidebar.invite.*, invitations.*)

Files

• New services: WorkspacesService.ts, TeamsService.ts, InvitationsService.ts, WorkspaceApiKeysService.ts
• New store: workspaceStore.ts; new hook: useWorkspace.ts
• New components: WorkspaceSwitcher, CreateWorkspaceDialog, InviteTeammateDialog, AcceptInvitationModal, WorkspaceSection, WorkspaceMembersTab, WorkspaceTeamsTab, WorkspaceBillingTab, WorkspaceDeveloperTab
• Modified: ControlPanelSidebar, ControlPanel, SettingsModal, SettingsPage, main.js, preload.js, electron.ts, all 10 translation.json

Premium-feel rules followed

• Members table is two-column max (identity + role+actions), 56px row height, 1px divider, no zebra striping
• Role dropdown uses the existing select primitive — no custom popover
• Empty states are minimal: small icon + one-line description + single primary CTA
• All copy is sentence case
• Spacing matches HistoryView.tsx (px-4 pt-4 pb-6 / max-w-3xl mx-auto)

Deferred

• Local SQLite migration to add workspace_id/team_id columns to the notes/folders tables — backwards-compat-safe to do later since cloud columns are nullable

Test plan

• First-time user (no workspaces): sidebar shows "Create workspace"; Settings → Workspace shows empty state with CTA
• Create a workspace → switcher updates, Settings sub-tabs populate
• Invite by email → seat counter increments → Stripe customer/sub created server-side
• Accept invitation via deep link from another machine → workspace appears in switcher
• Switch between workspaces — sidebar tabs re-scope, no flicker
• Mint a workspace API key, copy via the one-time reveal modal, verify it works against the API
• Switch i18n locale and verify all new strings render