Docs: full README rewrite + gui_client.py module docstring update

README now covers:
- Updated diff-mode section (self-describing protocol, no _diff marker)
- Full GUI section with Connector/Dashboard/Plot tab descriptions
- Plot mouse interactions table (scroll, Shift+scroll, drag)
- Module reference for all server/, utils/, and gui_client classes
- --dry flag and all credential-file keys documented

gui_client.py module docstring updated to list tabs and mouse interactions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gui_client.py

@@ -2,13 +2,20 @@
 """
 WeConnect GUI client.
 
-Connects to the collect.py TCP push server and displays live data.
+Connects to the collect.py TCP push server and displays live vehicle data.
 
 Tabs
 ----
-Connector  — server address, connect / disconnect, status
-Dashboard  — live tree view of the latest snapshot
-Plot       — time-series charts of all physical {value, unit} fields
+Connector  — host / port / diff-mode form; connect / disconnect
+Dashboard  — live tree view of the latest snapshot (domain → object → field)
+Plot       — 8 independent time-series plots in a scrollable 4×2 grid
+
+Plot interactions
+-----------------
+Scroll wheel          — zoom X axis in/out, centred on cursor
+Shift + scroll wheel  — zoom Y axis in/out, centred on cursor
+Click + drag          — pan
+Crosshair + tooltip   — dashed vertical line + floating value readout per trace
 """
 
 import json