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/.dockerignore

@@ -0,0 +1,45 @@
+**/*.dump
+**/*.lock
+**/*.log
+**/*.swo
+**/*.swp
+**/*.tmp
+**/*~
+**/.cache
+**/.dev.vars
+**/.DS_Store
+**/.env
+**/.env.*.local
+**/.env.local
+**/.git
+**/.idea
+**/.pnpm-store
+**/.rebar
+**/.rebar3
+**/.turbo
+**/.vscode
+**/_build
+**/_checkouts
+**/_vendor
+**/build
+**/certificates
+**/coverage
+**/dist
+**/erl_crash.dump
+**/generated
+**/log
+**/logs
+**/node_modules
+**/npm-debug.log*
+**/pnpm-debug.log*
+**/rebar3.crashdump
+**/target
+**/Thumbs.db
+**/yarn-debug.log*
+**/yarn-error.log*
+/fluxer_app/src/data/emojis.json
+/fluxer_app/src/locales/*/messages.js
+dev
+!fluxer_app/dist
+!fluxer_app/dist/**
+!fluxer_devops/cassandra/migrations