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/scripts/dev_fluxer_app.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+script_dir="$(cd "$(dirname "$0")" && pwd)"
+repo_root="$(cd "$script_dir/.." && pwd)"
+app_dir="$repo_root/fluxer_app"
+
+shutting_down=0
+child_pid=""
+
+shutdown() {
+	shutting_down=1
+	if [ -n "$child_pid" ] && kill -0 "$child_pid" 2>/dev/null; then
+		kill -TERM "$child_pid" 2>/dev/null || true
+		wait "$child_pid" 2>/dev/null || true
+	fi
+	exit 0
+}
+
+trap shutdown INT TERM
+
+(
+	cd "$app_dir"
+	./node_modules/.bin/tsx scripts/DevServer.tsx
+) &
+child_pid=$!
+
+wait "$child_pid"
+status=$?
+
+if [ "$shutting_down" -eq 1 ]; then
+	exit 0
+fi
+
+exit "$status"