docs: one ingress line in the architecture diagram, QQ through AstrBot

The separate NapCat door is gone from the drawing: QQ enters through
AstrBot like every other platform, which is the deployment the README
describes, and the forwarder box now says so. The reply path label is
just the HTTP response.

Author: wangkant

CHANGELOG.md

@@ -262,8 +262,8 @@ that fails without it.
   The README demo animation shows two lines of the room's chat above each
   incoming message and grows from two scenes to four: reply, pass, a reply
   that saves a memory, and a direct call answered with a sticker.
-  The architecture diagram is redrawn: both ingress doors (`/webhook/gateway`
-  via AstrBot, `/webhook/qq` via NapCat) converge on one five-stage path, the
+  The architecture diagram is redrawn: every platform, QQ included via NapCat,
+  enters through AstrBot and `/webhook/gateway` into one five-stage path, the
   learning column runs bottom-up from signals to promoted views and hot-reloads
   into prompt assembly, every arrow is labelled, and nothing overflows its box.