fix: unpair without changing the shade on the web server task

queueUnpairShade cleared shade->paired on the async_tcp task while loop()
owns the shade.  A second unpair queued before the first ran recorded
wasPaired=false and, if its Prog was refused, put back the wrong value.
The shade is now only changed by loop() once the Prog is queued, and the
response reports paired=false through a serializeShade overload instead.

No native test: Web.cpp can't be built by the native env.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/WebCommand.h

@@ -36,7 +36,6 @@ struct web_command_t {
     int8_t tiltPosition;    // for setPositions/tilt
     int8_t sunny;           // for sensor
     int8_t windy;           // for sensor
-    bool wasPaired;         // for unpair, restored if the Prog can't be sent
 };
 
 // Only setting positions never goes on air.