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_docs/schemas/events/USER_UPDATE.json

@@ -0,0 +1,11 @@
+{
+	"$schema": "https://json-schema.org/draft/2020-12/schema",
+	"name": "USER_UPDATE",
+	"description": "Properties about the current user changed.",
+	"scope": "presence",
+	"dispatchedBy": ["PATCH /users/@me", "PATCH /users/@me/profile"],
+	"payload": {
+		"$ref": "UserPrivateResponse",
+		"description": "The updated user object"
+	}
+}