feat(onboarding): guide users through the Gmail example

[Shreyasshukla957]

Summary

• add a Gmail-first onboarding route that lets new organizations choose and quick-add an app before creating their first agent
• provide a guided MCP practice path for building a Gmail UI, a cancellable five-minute workflow, an approval-gated Gmail skill, and thread notes
• retain the standard integration setup outside onboarding and record user-confirmed progress without claiming to inspect an external agent

Validation

• bun run lint
• bun run typecheck (45 workspace tasks)
• bun run test -- src/web/onboarding-progress.test.ts in apps/cloud (2 tests)
• bun run test -- src/api/analytics.test.ts in packages/react (6 tests)
• bun run build in packages/react
• bunx oxfmt --check on all changed source files
• git diff --check origin/main...HEAD

Local limitations

• The full non-E2E suite reaches pre-existing Windows portability failures in runtime-workerd-subprocess involving POSIX paths, Unix file permissions, and process PID reuse.
• The cloud browser harness cannot boot on Windows because apps/cloud/scripts/dev-db.ts invokes POSIX lsof ... || true; it also reaches an existing Vite TypeScript loader issue. The focused unit tests above cover the added progress and analytics logic.