Port Brave Sync server to Rust

Use SQLite for persistence and generate Rust protobuf bindings at build time.

Add Docker image support for containerized deployment.

Co-Authored-By: codex <[email protected]>

docker-entrypoint.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+set -eu
+
+data_dir="${SQLITE_PATH%/*}"
+if [ "$data_dir" = "$SQLITE_PATH" ]; then
+	data_dir="/var/lib/brave-sync"
+fi
+
+mkdir -p "$data_dir"
+chown -R brave-sync:brave-sync "$data_dir"
+
+exec gosu brave-sync "$@"