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.

.gitignore

@@ -6,6 +6,8 @@ dist/
 .env
 .env.local
 apps/*/dist/
+apps/*/out/
+apps/*/release/
 apps/*/node_modules/
 apps/*/.output/
 apps/*/.wxt/
@@ -15,4 +17,4 @@ apps/*/firefox-mv*/
 .superpowers/*
 .playwright-mcp/*
 *.log
-*.tmp
+*.tmp