fix(wasm): remove prefill sleep — restores ASYNCIFY token streaming (#33)

The emscripten_sleep(0) added to quant.h's prefill loop (PR #30)
broke ASYNCIFY for the entire quant_generate call. The call stack
during tq_forward() is too deep (matmul → SIMD kernels) for
ASYNCIFY to unwind/rewind — it silently fails and the generation
callback's sleep stops working too.

Fix: remove prefill sleep entirely. The prefill blocks the browser
for a few seconds (unavoidable without a step-by-step API), but
"Thinking..." is shown before via requestAnimationFrame. Token
streaming during generation works again.

Also: pthreads removed (PR #32) to avoid pthreads+ASYNCIFY
conflict, build.sh now uses single-thread SIMD + ASYNCIFY only.

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

Author: unamedkr

quant.h

@@ -15462,14 +15462,13 @@ int tq_generate(tq_model_t* model, tq_tokenizer_t* tokenizer,
     }
 
     /* Prefill: process all prompt tokens.
-     * On Emscripten with ASYNCIFY, yield every 2 tokens so the browser
-     * can repaint (shows "Thinking..." and avoids "page unresponsive"). */
+     * NOTE: No emscripten_sleep() here — the call stack during tq_forward()
+     * is too deep for ASYNCIFY to unwind (matmul → SIMD kernels). Adding
+     * sleep here breaks ASYNCIFY for the entire generate call, including
+     * the token streaming callback. The browser shows "Thinking..." via
+     * requestAnimationFrame before entering this blocking prefill. */
     for (int i = 0; i < n_prompt; i++) {
         tq_forward(model, state, prompt_tokens[i], i);
-#ifdef __EMSCRIPTEN__
-        extern void emscripten_sleep(unsigned int ms);
-        if (i % 2 == 1) emscripten_sleep(0);
-#endif
     }
 
     /* Repetition penalty setup */