add --bundle flag for self-contained IIFE output

elc --target=js --bundle source.el > output.js produces a single file
with no import statement that can drop directly into a <script> tag.

How it works:
  - detect_bundle() reads the --bundle flag from argv
  - resolve_runtime_path() looks for el_runtime.js next to the source file
  - compile_js_with_bundle() reads the runtime, calls codegen_js_bundle()
  - codegen_js_inner(bundle_mode=true):
    - emits ;(function() { "use strict"; at the top
    - inlines the runtime content (stripping ES export statements which
      are invalid inside an IIFE via js_strip_es_exports())
    - skips the const {...} = globalThis.__el destructure -- the inlined
      function declarations are already in scope within the IIFE
    - closes with })(); after main()

Usage: elc --target=js --bundle app.el > app.js
       Place el_runtime.js in the same directory as app.el.

el-compiler/src/compiler.el

@@ -29,7 +29,7 @@ fn compile(source: String) -> String {
     codegen(stmts, source)
 }
 
-// compile_js — full pipeline (JS target): source string -> JS source string
+// compile_js — full pipeline (JS target, module mode): source string -> JS source string
 fn compile_js(source: String) -> String {
     let tokens: [Map<String, Any>] = lex(source)
     let stmts: [Map<String, Any>] = parse(tokens)
@@ -38,6 +38,20 @@ fn compile_js(source: String) -> String {
     codegen_js(stmts, source)
 }
 
+// compile_js_with_bundle — JS target in bundle mode.
+// Reads el_runtime.js from runtime_path and inlines it inside an IIFE.
+fn compile_js_with_bundle(source: String, runtime_path: String) -> String {
+    let tokens: [Map<String, Any>] = lex(source)
+    let stmts: [Map<String, Any>] = parse(tokens)
+    el_release(tokens)
+    let runtime_content: String = fs_read(runtime_path)
+    if str_eq(runtime_content, "") {
+        println("el-compiler: warning: --bundle: could not read runtime at " + runtime_path)
+        println("el-compiler: warning: bundle output will be incomplete")
+    }
+    codegen_js_bundle(stmts, source, runtime_content)
+}
+
 // compile_dispatch — pick a backend based on the requested target.
 //   tgt = "c"  | "js"
 // (The parameter is named `tgt` because `target` is a reserved keyword
@@ -48,6 +62,12 @@ fn compile_dispatch(tgt: String, source: String) -> String {
     compile(source)
 }
 
+// compile_dispatch_bundle — like compile_dispatch but bundle mode for JS.
+fn compile_dispatch_bundle(tgt: String, source: String, runtime_path: String) -> String {
+    if str_eq(tgt, "js") { return compile_js_with_bundle(source, runtime_path) }
+    compile(source)
+}
+
 // Detect a `--target=<lang>` flag in argv and return the target.
 // Returns "c" if none specified or unrecognized.
 fn detect_target(argv: [String]) -> String {
@@ -91,6 +111,32 @@ fn detect_emit_header(argv: [String]) -> Bool {
     return false
 }
 
+// Detect --bundle flag in argv.
+fn detect_bundle(argv: [String]) -> Bool {
+    let n: Int = native_list_len(argv)
+    let i = 0
+    while i < n {
+        let a: String = native_list_get(argv, i)
+        if str_eq(a, "--bundle") { return true }
+        let i = i + 1
+    }
+    return false
+}
+
+// Resolve the runtime path for --bundle mode.
+// Looks for el_runtime.js next to the source file first;
+// if not found there, looks next to the elc binary itself.
+// Returns "" if not found anywhere (caller emits a warning).
+fn resolve_runtime_path(src_path: String) -> String {
+    let src_dir: String = dirname_of(src_path)
+    let candidate: String = src_dir + "/el_runtime.js"
+    let existing: String = fs_read(candidate)
+    if !str_eq(existing, "") {
+        return candidate
+    }
+    return ""
+}
+
 // Reconstruct an El type annotation string from a parsed type node.
 fn type_node_to_el(t: Map<String, Any>) -> String {
     let k: String = t["kind"]
@@ -251,10 +297,12 @@ fn resolve_imports(src_path: String) -> String {
 
 // main — CLI entry point.
 //
-//   elc <source.el>                            # emit C to stdout
-//   elc --target=js <source.el>                # emit JS to stdout
-//   elc --target=c  <source.el> <out.c>        # write C to file
-//   elc --target=js <source.el> <out.js>       # write JS to file
+//   elc <source.el>                               # emit C to stdout
+//   elc --target=js <source.el>                   # emit JS (module) to stdout
+//   elc --target=js --bundle <source.el>          # emit self-contained JS (IIFE) to stdout
+//   elc --target=c  <source.el> <out.c>           # write C to file
+//   elc --target=js <source.el> <out.js>          # write JS to file
+//   elc --target=js --bundle <source.el> <out.js> # write bundled JS to file
 fn main() -> Void {
     let argv: [String] = args()
     // Use `tgt` not `target`: `target` is a reserved keyword in the lexer
@@ -262,10 +310,11 @@ fn main() -> Void {
     // because the function-name position has no token-class restriction.
     let tgt: String = detect_target(argv)
     let do_emit_header: Bool = detect_emit_header(argv)
+    let do_bundle: Bool = detect_bundle(argv)
     let positional: [String] = strip_flags(argv)
     let argc: Int = native_list_len(positional)
     if argc < 1 {
-        println("el-compiler: usage: elc [--target=c|js] [--emit-header] <source.el> [<output>]")
+        println("el-compiler: usage: elc [--target=c|js] [--bundle] [--emit-header] <source.el> [<output>]")
         exit(1)
     }
     let src_path: String = native_list_get(positional, 0)
@@ -283,7 +332,13 @@ fn main() -> Void {
     }
 
     let source: String = resolve_imports(src_path)
-    let out: String = compile_dispatch(tgt, source)
+    let out: String = ""
+    if do_bundle {
+        let runtime_path: String = resolve_runtime_path(src_path)
+        let out = compile_dispatch_bundle(tgt, source, runtime_path)
+    } else {
+        let out = compile_dispatch(tgt, source)
+    }
     if argc >= 2 {
         let out_path: String = native_list_get(positional, 1)
         let ok: Bool = fs_write(out_path, out)