fix: JS const _ duplication and hardcoded version string

- JS backend now emits wildcard let bindings as side-effect statements
  instead of const _ declarations, fixing SyntaxError on multiple let _ = ...
- Version string now uses env!("CARGO_PKG_VERSION") to auto-sync with Cargo.toml
- Add -lm linker flag for math library support

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.rs

@@ -37,7 +37,7 @@ use std::borrow::Cow;
 use std::collections::HashSet;
 use typechecker::TypeChecker;
 
-const VERSION: &str = "0.1.0";
+const VERSION: &str = env!("CARGO_PKG_VERSION");
 
 const HELP: &str = r#"
 Lux - A functional language with first-class effects
@@ -902,6 +902,7 @@ fn compile_to_c(path: &str, output_path: Option<&str>, run_after: bool, emit_c:
         .args(["-O2", "-o"])
         .arg(&output_bin)
         .arg(&temp_c)
+        .arg("-lm")
         .output();
 
     match compile_result {