feat(web): stream chat replies token-by-token (M3)

- llm.chat_call_stream: streaming generator for all 3 backends (Ollama NDJSON,
  OpenAI/MI50 SSE), accumulating tool-call fragments by index.
- chat.respond_stream: mirrors respond()'s tool loop and persistence/compaction,
  yielding ("delta", text) / ("tool", name) / ("done", reply).
- POST /v1/chat/stream: SSE endpoint; blocking generator bridged to async via a
  worker thread + asyncio.Queue. Old completions endpoint kept as fallback.
- Client streams into a live bubble with a blinking caret; rAF-throttled render
  (no full re-parse per token) and instant scroll during stream — fixes iOS
  Safari ghosting from per-token smooth-scroll. Falls back to the blocking
  endpoint only if nothing streamed (no double-persist).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyra/web/static/style.css

@@ -139,7 +139,9 @@ button:hover, select:hover {
   display: flex;
   flex-direction: column;
   gap: 8px;
-  scroll-behavior: smooth;
+  /* No CSS smooth-scroll: during streaming, per-token smooth scrolls pile up and
+     iOS Safari leaves ghost paint frames. Smooth is applied explicitly in JS where
+     it's a one-shot (load/finalize). */
 }
 
 /* Messages */
@@ -1090,6 +1092,16 @@ select:hover {
 }
 .msg.assistant pre code { background: none; padding: 0; font-size: 0.85em; }
 
+/* Streaming: a blinking caret while tokens arrive (and a min-size while empty). */
+.msg.assistant.streaming { min-width: 1.4em; min-height: 1.1em; }
+.msg.assistant.streaming::after {
+  content: "▋";
+  margin-left: 1px;
+  color: var(--accent);
+  animation: caretBlink 1s steps(1) infinite;
+}
+@keyframes caretBlink { 0%, 50% { opacity: 0.85; } 50.01%, 100% { opacity: 0; } }
+
 /* Behind-the-scenes 👍/👎 feedback (fine-tune signal) — subtle until hovered. */
 .rate-bar { display: flex; gap: 6px; margin-top: 7px; opacity: 0.3; transition: opacity .15s; }
 .msg.assistant:hover .rate-bar { opacity: 0.85; }