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/README.md

@@ -0,0 +1,31 @@
+# Fluxer Desktop
+
+Electron desktop client for Fluxer. Wraps the web application with native platform integrations including notifications, global shortcuts, screen sharing, passkeys, and auto-updates.
+
+## Configuration
+
+The desktop client reads an optional `settings.json` file from the user data directory on startup. If the file does not exist, defaults are used.
+
+### User data directory locations
+
+| Platform | Stable                                               | Canary                                                     |
+| -------- | ---------------------------------------------------- | ---------------------------------------------------------- |
+| Windows  | `%APPDATA%\fluxer\settings.json`                     | `%APPDATA%\fluxercanary\settings.json`                     |
+| macOS    | `~/Library/Application Support/fluxer/settings.json` | `~/Library/Application Support/fluxercanary/settings.json` |
+| Linux    | `~/.config/fluxer/settings.json`                     | `~/.config/fluxercanary/settings.json`                     |
+
+### Available options
+
+| Key       | Type   | Default (Stable)         | Default (Canary)                | Description                         |
+| --------- | ------ | ------------------------ | ------------------------------- | ----------------------------------- |
+| `app_url` | string | `https://web.fluxer.app` | `https://web.canary.fluxer.app` | URL of the web application to load. |
+
+### Example
+
+```json
+{
+  "app_url": "https://my-instance.example.com"
+}
+```
+
+When `app_url` is set, the desktop client loads that URL instead of the default and treats its origin as trusted for permissions, navigation, and the local RPC server.