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/.vscode/settings.json

@@ -0,0 +1,5 @@
+{
+	"typescript.preferences.includePackageJsonAutoImports": "auto",
+	"typescript.suggest.autoImports": true,
+	"typescript.experimental.useTsgo": true
+}