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/scripts/ci/workflows/sync_static.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+import pathlib
+import sys
+
+sys.path.append(str(pathlib.Path(__file__).resolve().parents[1]))
+
+from ci_steps import INSTALL_RCLONE_SCRIPT, rclone_config_script
+from ci_workflow import parse_step_env_args
+from ci_utils import run_step
+
+
+STEPS: dict[str, str] = {
+    "install_rclone": INSTALL_RCLONE_SCRIPT,
+    "push": rclone_config_script(
+        endpoint="$RCLONE_ENDPOINT",
+        acl="private",
+        expand_vars=True,
+    )
+    + """
+mkdir -p "$RCLONE_SOURCE_DIR"
+rclone sync "$RCLONE_SOURCE" "$RCLONE_REMOTE:$RCLONE_BUCKET" --create-empty-src-dirs --exclude "assets/**"
+""",
+}
+
+
+def main() -> int:
+    args = parse_step_env_args()
+    run_step(STEPS, args.step)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())