Add --version flag to CLI (#189)

Add support for --version (-V) flag to display the current version.
The version is now available on-demand via CLI flag in addition to
being displayed during server startup.

Updates:
- Add version attribute to CLI struct using clap's built-in version support
- Update README.md to document the new --version flag and usage

Resolves the common CLI expectation of having a version flag.

Author: SimonKaran13

README.md

@@ -52,7 +52,8 @@ Commands:
   help   Print this message or the help of the given subcommand(s)
 
 Options:
-  -h, --help  Print help
+  -h, --help     Print help
+  -V, --version  Print version
 ```
 
 ### Using the stdio protocol

src/cli.rs

@@ -24,6 +24,7 @@ use std::path::PathBuf;
 
 /// Elastic MCP server
 #[derive(Debug, Parser)]
+#[command(version)]
 pub struct Cli {
     /// Container mode: change default http address, rewrite localhost to the host's address
     #[clap(global=true, long, env = "CONTAINER_MODE")]