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/config/livekit.example.yaml

@@ -0,0 +1,16 @@
+port: 7880
+
+keys:
+  '<replace-with-api-key>': '<replace-with-api-secret>'
+
+rtc:
+  tcp_port: 7881
+
+turn:
+  enabled: true
+  udp_port: 3478
+
+room:
+  auto_create: true
+  max_participants: 100
+  empty_timeout: 300