feat: add local self-host installer

[Uarmagan]

Summary

• Add a local Docker Compose self-host installer for Compass.
• Run the full local stack: web, backend, MongoDB, SuperTokens Core, and internal Postgres for SuperTokens auth storage.
• Add local helper commands for start, stop, restart, rebuild, logs, status, update, and open.
• Update README and self-hosting docs to lead with the installer and clarify local-only Google behavior.

Validation

Passed:

• Full installer smoke test with isolated Compose project compasssmoke
  • Docker images built
  • backend /api/health returned ok
  • web root and /day fallback returned the app shell
  • helper status listed web, backend, mongo, supertokens, and supertokens-db
  • only 127.0.0.1:9080 and 127.0.0.1:3000 were exposed
  • smoke stack was stopped afterward
• sh -n self-host/install.sh
• sh -n self-host/compass
• docker compose --env-file self-host/.env.example -f self-host/docker-compose.yml config
• bun run test:core
• bun run test:backend (rerun by itself after the parallel Mongo config race)
• bun run test:scripts
• git diff --check origin/main...HEAD

Known existing failures:

• bun run test:web fails in the current web test harness with missing browser/test globals such as document, MouseEvent, jest, and expect.
• bun run lint fails on existing repo-wide Biome findings outside this installer work.
• Running backend and scripts tests in parallel can race on the shared Jest Mongo globalConfig.json; both pass when run separately.

Notes

• The installer does not delete Docker volumes.
• Google Calendar sync is not configured by the local installer. Custom Google OAuth values require ./compass rebuild, and ongoing Google Calendar watch notifications require HTTPS/public backend setup outside this local-only path.
• If an install folder is lost but Docker volumes remain, the installer now stops before generating incompatible new secrets and tells the user to restore .env, choose another COMPOSE_PROJECT_NAME, or intentionally remove old volumes themselves.