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_integration/docker/livekit.yaml

@@ -0,0 +1,19 @@
+port: 7880
+
+keys:
+  'devkey': 'devsecret'
+
+rtc:
+  tcp_port: 7881
+
+webhook:
+  api_key: 'devkey'
+  urls:
+    - ''
+
+room:
+  auto_create: true
+  max_participants: 100
+  empty_timeout: 300
+
+development: true