feat(enterprise): add workspace selection UI

[Gracker]

Summary

• add SmartPerfetto frontend request context helpers for tenant/user/workspace/window headers, storage namespaces, and workspace-scoped API URLs
• add workspace selection in the AI Assistant settings UI and expose the active workspace in the panel header
• scope assistant settings, sessions, pinned state, analysis mode, and pending trace recovery by user/workspace/window as appropriate
• route assistant, provider, trace upload, trace picker, feedback, and critical path calls through workspace-aware APIs where applicable
• refresh the committed frontend bundle for ./start.sh and Docker users

Validation

• PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run test -- --test-filter 'SmartPerfetto frontend request context|SessionManager|Agent SSE transport' in perfetto/ui
• PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run build -- --typecheck --no-depscheck in perfetto/ui
• PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run build -- --no-depscheck in perfetto/ui
• dev-mode Playwright smoke: changed workspace from default-workspace to workspace-ui-check, verified namespaced storage keys and X-Tenant-Id / X-Workspace-Id / X-Window-Id request headers
• git diff --check
• PATH="$HOME/.nvm/versions/node/v24.15.0/bin:$PATH" npm run verify:pr