feat(chat): stream model thinking over SSE and show it in a collapsible block

README.md

@@ -87,6 +87,21 @@ uv run uvicorn app.main:app --reload
   anonymous visitors see a sign-in gate instead (the catalog is what the
   login locks; the document viewer itself stays open to everyone).
 
+## Thinking
+
+The self-hosted `turbo` model reasons before it answers. That reasoning is
+streamed with the turn as `thinking` SSE events and shown in a
+**collapsible "Thinking" block** above the answer bubble: it opens and
+fills in live while the model thinks, tucks itself away the moment the
+first answer token lands, and stays click-toggleable afterwards. Thinking
+persists with the message, so a reloaded conversation restores the block
+(collapsed) alongside the answer. How much the model thinks — or whether
+it thinks at all — is the model's call: turns without reasoning render
+exactly as before.
+
+To hide it, set `BOR_STREAM_THINKING=0` — the `thinking` events stop
+(the per-turn log line still counts `thinking_chars`).
+
 ## Admin & sign-in
 
 Brain of Reese has exactly **one account: the admin (you)**. Signing in