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/pnpm-workspace.yaml

@@ -0,0 +1,17 @@
+allowBuilds:
+  electron-winstaller: true
+  electron: true
+  esbuild: true
+  node-mac-permissions: true
+  uiohook-napi: true
+allowedDeprecatedVersions:
+  '@electron-webauthn/native': 0.0.6
+  boolean: 3.2.0
+  glob: 7.2.3
+  inflight: 1.0.6
+  rimraf: 2.6.3
+  tar: 6.2.1
+blockExoticSubdeps: true
+minimumReleaseAge: 1440
+strictDepBuilds: true
+trustPolicy: no-downgrade