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/packages/constants/package.json

@@ -0,0 +1,15 @@
+{
+	"name": "@fluxer/constants",
+	"version": "0.0.0",
+	"private": true,
+	"type": "module",
+	"exports": {
+		"./*": "./*"
+	},
+	"scripts": {
+		"typecheck": "tsgo --noEmit"
+	},
+	"devDependencies": {
+		"@typescript/native-preview": "catalog:"
+	}
+}