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_desktop/packaging/homebrew/README.md

@@ -0,0 +1,25 @@
+# Fluxer Homebrew cask
+
+Homebrew cask definition for installing Fluxer on macOS.
+
+## Placeholders
+
+The `version` and `sha256` fields are set to placeholder values. Update them before publishing or submitting to a tap.
+
+## Livecheck
+
+The cask includes a `livecheck` block that queries the Fluxer download API for the latest stable version. Homebrew's automated tooling uses this to detect new releases.
+
+## Testing locally
+
+```bash
+brew install --cask ./fluxer.rb
+```
+
+## Fetching the latest version
+
+```bash
+curl -s https://api.fluxer.app/dl/desktop/stable/darwin/arm64/latest | jq
+```
+
+This returns a JSON object containing `version`, `pub_date`, and `files` with download URLs and SHA256 checksums for each format.