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_relay/config/relay.json

@@ -0,0 +1,24 @@
+{
+	"$schema": "../../packages/config/src/ConfigSchema.json",
+	"services": {
+		"relay": {
+			"port": 8090,
+			"upstream_api_host": "localhost:8080",
+			"upstream_gateway_host": "localhost:8081",
+			"upstream_use_tls": false,
+			"max_connections_per_instance": 1000,
+			"connection_timeout_ms": 30000,
+			"idle_timeout_ms": 120000,
+			"allowed_origins": [],
+			"logger_level": "info"
+		}
+	},
+	"federation": {
+		"instance_domain": "localhost"
+	},
+	"telemetry": {
+		"enabled": false,
+		"otlp_endpoint": "",
+		"service_name": "fluxer-relay"
+	}
+}

fluxer/fluxer_relay/config/sys.config.src

@@ -0,0 +1,24 @@
+[
+    {fluxer_relay, []},
+    {kernel, [
+        {logger_level, info},
+        {logger, [
+            {handler, default, logger_std_h, #{
+                level => info,
+                config => #{
+                    type => standard_io
+                }
+            }}
+        ]},
+        {inet_backend, socket}
+    ]},
+    {sasl, [
+        {errlog_type, error}
+    ]},
+    {lager, [
+        {handlers, [
+            {lager_console_backend, [{level, info}]}
+        ]},
+        {crash_log, false}
+    ]}
+].

fluxer/fluxer_relay/config/vm.args.src

@@ -0,0 +1,12 @@
+-name ${FLUXER_RELAY_NODE_NAME}
++K true
++A30
+-env ERL_MAX_PORTS 4096
+-env ERL_PROCESSES 262144
++P 262144
++Q 65536
++S 4:4
++zdbbl 32768
+-kernel logger_level info
+-kernel inet_backend socket
+-start_epmd false