feat: add Rust binary calculator example

First example of the binary server type — a compiled Rust MCP server
packaged as an MCPB. Based on the official Rust SDK calculator example
(rmcp 1.2.0, 2 tools: sum/sub, ~80 LOC).

Includes Cargo.toml, Dockerfile for Docker-based builds, .mcpbignore
to exclude source from the bundle, and README with build/pack/test
instructions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/calculator-rust/README.md

@@ -0,0 +1,87 @@
+# Calculator Rust Binary Example
+
+Demonstrates packaging a compiled Rust binary as an MCP Bundle using the `binary` server type. Based on the [official Rust MCP SDK calculator example](https://github.com/modelcontextprotocol/rust-sdk/tree/main/examples/servers).
+
+## What is Binary Server Type?
+
+Unlike `node` or `uv` server types where the source code is bundled and executed by a runtime, the `binary` server type packages a pre-compiled native executable. This is useful for:
+
+- Rust, Go, C/C++ MCP servers
+- Performance-sensitive workloads
+- Servers with no runtime dependencies
+
+The tradeoff is that binaries are platform-specific — you need a separate build for each target OS/architecture.
+
+## Structure
+
+```
+calculator-rust/
+├── manifest.json       # server.type = "binary"
+├── Cargo.toml          # Rust project
+├── Dockerfile          # Build via Docker
+├── .mcpbignore         # Exclude source from bundle
+├── .gitignore          # Exclude build artifacts
+└── src/
+    └── main.rs         # Calculator MCP server (~80 LOC)
+```
+
+After building, the `server/` directory is created with the compiled binary.
+
+## Building
+
+### Native (requires Rust 1.85+)
+
+```bash
+cd examples/calculator-rust
+cargo build --release
+mkdir -p server
+cp target/release/mcp-calculator server/
+```
+
+### Docker (no local Rust required)
+
+```bash
+cd examples/calculator-rust
+docker build -t mcp-calculator .
+# Extract the binary (linux only)
+docker create --name calc mcp-calculator
+docker cp calc:/mcp-calculator server/mcp-calculator
+docker rm calc
+chmod +x server/mcp-calculator
+```
+
+## Packing
+
+```bash
+mcpb pack examples/calculator-rust
+```
+
+The `.mcpbignore` file excludes source code and build artifacts — only `manifest.json` and `server/mcp-calculator` end up in the bundle.
+
+## Testing
+
+```bash
+# MCP protocol handshake
+echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}' \
+  | ./server/mcp-calculator
+
+# Tool call
+(printf '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}\n'
+printf '{"jsonrpc":"2.0","method":"notifications/initialized"}\n'
+printf '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"sum","arguments":{"a":3,"b":4}}}\n'
+sleep 1) | ./server/mcp-calculator
+```
+
+Expected: `sum(3, 4)` returns `{"text":"7"}`.
+
+## Tools
+
+- **sum** — Calculate the sum of two numbers
+- **sub** — Calculate the difference of two numbers
+
+## Notes
+
+- Binary size: ~2.5 MB (stripped, LTO enabled)
+- The `Cargo.toml` uses `edition = "2024"` (Rust 1.85+)
+- Logs are written to stderr via `tracing`, so they don't interfere with MCP's stdio transport
+- Uses the [rmcp](https://crates.io/crates/rmcp) crate (official Rust MCP SDK)