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]>

README.md

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+# Brave Sync Server v2 Rust Port
+
+Rust port of the Brave Sync v2 command server from `/home/user/go-sync`.
+
+The server exposes:
+
+- `GET /`
+- `GET /health-check`
+- `POST /v2/command/`
+- `GET /metrics`
+
+## Storage
+
+This port uses SQLite instead of DynamoDB. On startup it creates the required
+tables automatically.
+
+Environment variables:
+
+- `SQLITE_PATH`: SQLite database path. Defaults to `brave-sync.sqlite3`.
+- `LISTEN_ADDR`: HTTP listen address. Defaults to `0.0.0.0:8295`.
+- `BLOCKED_CLIENT_IDS`: comma-separated lowercase or uppercase client public key hex values.
+- `HIGH_DEVICE_LIMIT_CLIENT_IDS`: comma-separated client IDs allowed up to 100 active devices.
+
+## Build and Test
+
+```sh
+cargo test
+cargo run
+```
+
+## Docker
+
+```sh
+docker build -t brave-sync-rs .
+docker run --rm -p 8295:8295 -v brave-sync-data:/var/lib/brave-sync brave-sync-rs
+```
+
+For bind mounts, the container starts as root only long enough to create/chown
+the SQLite directory, then runs the server as the `brave-sync` user.
+
+The protobuf Rust bindings are generated at build time from
+`schema/protobuf/sync_pb`. A vendored `protoc` binary is used, so a system
+`protoc` install is not required.