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_devops/caddy/Caddyfile.global

@@ -0,0 +1,16 @@
+{
+	servers {
+		listener_wrappers {
+			proxy_protocol {
+				timeout 5s
+				allow 127.0.0.0/8
+				allow 10.0.0.0/8
+				allow 172.16.0.0/12
+				allow ::1/128
+			}
+			tls
+		}
+		trusted_proxies static private_ranges
+		trusted_proxies_strict
+	}
+}