Move scipy and matplotlib from server to demos requirements

Both are only used by scripts/demos — the server itself only needs numpy
(used by kalman.py, delay.py, tempSensorSim.py, hendiCtrl.py).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SH2D4LRuCnhLSzoYerAfJX

scripts/demos/requirements.txt

@@ -0,0 +1,3 @@
+numpy
+scipy
+matplotlib

server/requirements.txt

@@ -1,6 +1,4 @@
 numpy
-scipy
-matplotlib
 websockets==10.4
 dpath
 pyserial