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/config/config.schema.json

@@ -0,0 +1,4 @@
+{
+	"$schema": "https://json-schema.org/draft/2020-12/schema",
+	"$ref": "../packages/config/src/ConfigSchema.json"
+}