IO-aware eval for server dispatch + compile-modules timeout bump

sx_server.ml: the "eval" command now uses cek_run_with_io instead of
raw eval_expr. This handles import suspensions during eval-blob
(needed for .sx files with define-library/import wrappers).

compile-modules.js: timeout bumped 5min → 10min for sxbc compilation
with define-library overhead.

2608/2608 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/browser/compile-modules.js

@@ -88,7 +88,7 @@ const t1 = Date.now();
 const result = spawnSync(binPath, [], {
   input: fs.readFileSync(tmpFile),
   maxBuffer: 100 * 1024 * 1024, // 100MB
-  timeout: 300000, // 5 min
+  timeout: 600000, // 10 min
   stdio: ['pipe', 'pipe', 'pipe'],
 });