feat(desktop): implement workspace foundation + desktop-client skeleton

Plan 0 (workspaces): add workspaces + workspace_memberships schema, extend
JWT/Actor/claims with primary_workspace_id, seed default workspace per tenant,
thread workspace_id through tenant monitoring quota.

Plan A (desktop skeleton): new Electron app (apps/desktop-client) with main/
preload/renderer, shared Vue component package (packages/ui-shared), and server
surface — desktop client registration + token rotation + heartbeat, SSE task
event stream, desktop accounts/tasks/content handlers, publish job endpoint,
and supporting repositories, services, sqlc queries, and migrations.

Hard cutover per plan: remove browser-extension monitoring callback endpoints,
stub legacy media API in admin-web, and delete monitoring_callback_handler.go.

apps/desktop-client/electron-builder.yml

@@ -0,0 +1,18 @@
+appId: com.geo.rankly.desktop
+productName: GEO Rankly Desktop
+directories:
+  output: release
+files:
+  - out/**
+asar: true
+mac:
+  category: public.app-category.productivity
+  target:
+    - dmg
+    - zip
+win:
+  target:
+    - nsis
+linux:
+  target:
+    - AppImage