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/manifest.json

@@ -0,0 +1,36 @@
+{
+  "$schema": "../../dist/mcpb-manifest.schema.json",
+  "manifest_version": "0.3",
+  "name": "calculator-rust",
+  "display_name": "Calculator (Rust Binary)",
+  "version": "1.0.0",
+  "description": "A simple calculator MCP server compiled from Rust",
+  "long_description": "Demonstrates packaging a compiled Rust binary as an MCP Bundle using the binary server type. The server provides sum and sub tools for basic arithmetic. Based on the official Rust MCP SDK calculator example.",
+  "author": {
+    "name": "Model Context Protocol"
+  },
+  "server": {
+    "type": "binary",
+    "entry_point": "server/mcp-calculator",
+    "mcp_config": {
+      "command": "${__dirname}/server/mcp-calculator",
+      "args": [],
+      "env": {}
+    }
+  },
+  "tools": [
+    {
+      "name": "sum",
+      "description": "Calculate the sum of two numbers"
+    },
+    {
+      "name": "sub",
+      "description": "Calculate the difference of two numbers"
+    }
+  ],
+  "keywords": ["calculator", "rust", "binary", "example"],
+  "license": "Apache-2.0",
+  "compatibility": {
+    "platforms": ["darwin", "linux"]
+  }
+}