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/.ignore

@@ -0,0 +1,73 @@
+!fluxer_app/scripts/build
+*.tsbuildinfo
+**/*.beam
+**/*.css.d.ts
+**/*.dump
+**/dump.rdb
+**/*.iml
+**/*.lock
+**/*.log
+**/*.o
+**/*.plt
+**/*.source
+**/*.swo
+**/*.swp
+**/*.tmp
+**/*~
+**/.*cache
+**/.cache
+**/__pycache__
+**/.dev.vars
+**/.direnv
+.devenv.flake.nix
+**/.env
+**/.env.*.local
+**/.env.local
+**/.erlang.cookie
+**/.eunit
+**/.next
+**/.next/cache
+**/.pnp
+**/.pnp.js
+**/.pnpm-store
+**/.rebar
+**/.rebar3
+**/.source
+**/.swc
+**/.turbo
+**/.vercel
+**/_build
+**/_checkouts
+**/_vendor
+**/build
+**/certificates
+**/coverage
+**/dist
+**/ebin
+**/erl_crash.dump
+**/fluxer.env
+**/generated
+**/log
+**/logs
+**/node_modules
+**/npm-debug.log*
+**/out
+**/pnpm-debug.log*
+**/rebar3.crashdump
+**/secrets.env
+**/target
+**/yarn-debug.log*
+**/yarn-error.log*
+/.fluxer/
+/fluxer_app/src/assets/emoji-sprites/
+/fluxer_app/src/locales/*/messages.js
+/fluxer_admin/public/static/app.css
+fluxer.yaml
+fluxer_app/dist/
+/fluxer_marketing/public/static/app.css
+/fluxer_server/data/
+fluxer_static
+geoip_data
+livekit.yaml
+next-env.d.ts
+/packages/marketing/public/static/app.css