add --minify and --obfuscate flags to elc JS pipeline

Adds two post-processing flags that produce production-ready browser JS in a
single elc invocation, replacing extract-js.py in the web product pipeline:

  elc --target=js --bundle --minify source.el > output.min.js
  elc --target=js --bundle --obfuscate source.el > output.obf.js

--minify shells out to terser (passes=2, no drop_console, drop_debugger).
--obfuscate shells out to javascript-obfuscator with the same options as the
old extract-js.py script. --obfuscate implies --minify.

Tool discovery: checks ./node_modules/.bin/, ../node_modules/.bin/ (monorepo),
then falls back to npx. Both flags require --target=js; passing either without
it exits 1 with a clear error.

Both tools receive a reserved-names list of globals referenced from HTML
onclick= attributes (neuronDemoToggle, signInWith, NEURON_CFG, etc.) so they
are not mangled.

Implementation adds stdout_to_file(path)/stdout_restore() builtins to the C
runtime so codegen's println-streamed output can be captured to a temp file
before being piped through the external tools. Temp files use
/tmp/elc-<pid>-<timestamp>.js naming and are cleaned up on success and failure.

Rebuilds dist/platform/elc and dist/platform/elc.c. Self-hosting verified.

el-compiler/runtime/el_runtime.c

@@ -155,6 +155,36 @@ el_val_t readline(void) {
     return el_wrap_str(el_strdup(buf));
 }
 
+/* ── stdout redirect helpers ─────────────────────────────────────────────── *
+ * Used by elc post-processing (--minify, --obfuscate): capture codegen       *
+ * output into a temp file, then pass it to the external tool.                */
+
+static int _stdout_saved_fd = -1;
+
+/* stdout_to_file(path) — redirect stdout to <path>. Returns 1 on success.   */
+el_val_t stdout_to_file(el_val_t pathv) {
+    const char* path = EL_CSTR(pathv);
+    if (!path || !*path) return (el_val_t)(int64_t)0;
+    fflush(stdout);
+    _stdout_saved_fd = dup(STDOUT_FILENO);
+    if (_stdout_saved_fd < 0) return (el_val_t)(int64_t)0;
+    int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
+    if (fd < 0) { close(_stdout_saved_fd); _stdout_saved_fd = -1; return (el_val_t)(int64_t)0; }
+    dup2(fd, STDOUT_FILENO);
+    close(fd);
+    return (el_val_t)(int64_t)1;
+}
+
+/* stdout_restore() — restore stdout from the saved fd. Returns 1 on success. */
+el_val_t stdout_restore(void) {
+    if (_stdout_saved_fd < 0) return (el_val_t)(int64_t)0;
+    fflush(stdout);
+    dup2(_stdout_saved_fd, STDOUT_FILENO);
+    close(_stdout_saved_fd);
+    _stdout_saved_fd = -1;
+    return (el_val_t)(int64_t)1;
+}
+
 /* ── String builtins ─────────────────────────────────────────────────────── */
 
 el_val_t el_str_concat(el_val_t av, el_val_t bv) {