feat: add fluxer upstream source and self-hosting documentation

- Clone of github.com/fluxerapp/fluxer (official upstream)
- SELF_HOSTING.md: full VM rebuild procedure, architecture overview,
  service reference, step-by-step setup, troubleshooting, seattle reference
- dev/.env.example: all env vars with secrets redacted and generation instructions
- dev/livekit.yaml: LiveKit config template with placeholder keys
- fluxer-seattle/: existing seattle deployment setup scripts

fluxer/.prettierignore

@@ -0,0 +1,22 @@
+*.log
+**/*.css.d.ts
+**/.cache
+**/.pnpm-store
+**/.swc
+**/.turbo
+**/node_modules
+**/package-lock.json
+**/pnpm-lock.yaml
+.fluxer/
+fluxer_app/dist
+fluxer_app/pkgs/libfluxcore
+fluxer_app/pkgs/libfluxcore/**
+fluxer_app/src/assets/emoji-sprites
+fluxer_app/src/locales/*/messages.js
+fluxer_app_proxy/assets
+fluxer_gateway/_build
+fluxer_marketing/build
+fluxer_static/**
+node_modules
+package-lock.json
+pnpm-lock.yaml