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/aur/README.md

@@ -0,0 +1,24 @@
+# Fluxer AUR package
+
+PKGBUILD for the `fluxer-bin` AUR binary package. This installs pre-built binaries rather than building from source, since Electron apps are impractical to compile within the AUR build system.
+
+## Placeholders
+
+The `pkgver` and `sha256sums` fields are set to placeholder values. Update them before publishing:
+
+- Run `updpkgsums` to fetch and fill checksums automatically.
+- Alternatively, query the latest version from the API and update manually.
+
+## Testing locally
+
+```bash
+makepkg -si
+```
+
+## Fetching the latest version
+
+```bash
+curl -s https://api.fluxer.app/dl/desktop/stable/linux/x64/latest | jq
+```
+
+This returns a JSON object containing `version`, `pub_date`, and `files` with download URLs and SHA256 checksums for each format.