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_process_entry.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if [ "$#" -lt 2 ]; then
+	echo "Usage: $0 <service_name> <command...>" >&2
+	exit 1
+fi
+
+service_name="$1"
+shift
+
+script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+repo_root="$(cd "$script_dir/.." && pwd)"
+
+runtime_dir="${DEVENV_RUNTIME:-${XDG_RUNTIME_DIR:-/tmp}}"
+lock_dir="${runtime_dir}/fluxer_dev_bootstrap.lock"
+stamp_file="${runtime_dir}/fluxer_dev_bootstrap.done"
+
+mkdir -p "$repo_root/dev/logs"
+
+if [ "${FLUXER_SKIP_BOOTSTRAP:-0}" != "1" ]; then
+	if [ "${FLUXER_FORCE_BOOTSTRAP:-0}" = "1" ] || [ ! -f "$stamp_file" ]; then
+		if mkdir "$lock_dir" 2>/dev/null; then
+			trap 'rmdir "$lock_dir" 2>/dev/null || true' EXIT
+
+			# Keep bootstrap output out of per-service logs.
+			rm -f "$stamp_file" 2>/dev/null || true
+			"$repo_root/scripts/dev_bootstrap.sh" >"$repo_root/dev/logs/bootstrap.log" 2>"$repo_root/dev/logs/bootstrap.err.log"
+
+			date -Is >"$stamp_file"
+			rmdir "$lock_dir" 2>/dev/null || true
+			trap - EXIT
+		else
+			# Another process is bootstrapping – wait for completion.
+			wait_started_at="$(date +%s)"
+			while [ ! -f "$stamp_file" ]; do
+				if [ "$(( $(date +%s) - wait_started_at ))" -gt 120 ]; then
+					echo "Timed out waiting for bootstrap to complete (service=$service_name)." >&2
+					echo "If this persists, stop the stack and remove ${lock_dir} and ${stamp_file}." >&2
+					exit 1
+				fi
+				sleep 0.2
+			done
+		fi
+	fi
+fi
+
+cd "$repo_root"
+exec "$@"