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/fluxer_devops/weblate/.env.example

@@ -0,0 +1,36 @@
+WEBLATE_SITE_DOMAIN=i18n.fluxer.app
+WEBLATE_SITE_TITLE=Fluxer Localization Platform
+WEBLATE_ADMIN_EMAIL=admin@fluxer.app
+WEBLATE_ADMIN_PASSWORD=
+WEBLATE_ADMIN_NAME=Fluxer Admin
+WEBLATE_SERVER_EMAIL=admin@fluxer.app
+WEBLATE_DEFAULT_FROM_EMAIL=noreply@fluxer.app
+
+WEBLATE_EMAIL_HOST=
+WEBLATE_EMAIL_PORT=587
+WEBLATE_EMAIL_USE_SSL=0
+WEBLATE_EMAIL_USE_TLS=1
+WEBLATE_EMAIL_HOST_USER=apikey
+WEBLATE_EMAIL_HOST_PASSWORD=
+
+WEBLATE_DB_PASSWORD=
+POSTGRES_DB=weblate
+POSTGRES_USER=weblate
+POSTGRES_PASSWORD=
+POSTGRES_HOST=weblate-postgres
+POSTGRES_PORT=5432
+
+VALKEY_PASSWORD=
+REDIS_HOST=valkey
+REDIS_PORT=6379
+REDIS_DB=1
+REDIS_PASSWORD=
+
+CACHE_URL=redis://:@valkey:6379/1
+BROKER_URL=redis://:@valkey:6379/2
+CELERY_BROKER_URL=redis://:@valkey:6379/2
+
+WEBLATE_SECURE_PROXY_SSL_HEADER=HTTP_X_FORWARDED_PROTO,https
+WEBLATE_ENABLE_HTTPS=1
+WEBLATE_IP_BEHIND_REVERSE_PROXY=1
+WEBLATE_IP_PROXY_HEADER=HTTP_X_FORWARDED_FOR