fix: review fixes for the OTA slot

- The field is hasOtaSlot, like hasEthernet and the other "has" bools.
- The web UI shows the device's reason for any failed upload, not only
  for /restore, so it shows "no OTA slot" from a page that missed the
  header. The update routes' 500 replies give Update.errorString()
  instead of an empty reason.
- Native: the writer leaves hasOtaSlot out when true and writes "os":0.
- e2e: header() next to uptime(); the test skips on firmware without
  the field instead of failing, and matches the reason loosely. The
  README says what the test sends.
- PROTOCOL.md and the comments name only the builds that exist.

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

data-src/js/model.js

@@ -140,7 +140,7 @@ ProtoModel.ITEMS = [
 // have it.
 ProtoModel.FIELDS = {
     header: ['maxRooms', 'maxShades', 'maxGroups', 'maxGroupedShades', 'maxLinkedRemotes', 'startingAddress', 'bitLength',
-        'proto', 'serverId', 'hostname', 'model', 'chipModel', 'otaSlot', 'fw', 'connType'],
+        'proto', 'serverId', 'hostname', 'model', 'chipModel', 'hasOtaSlot', 'fw', 'connType'],
     room: ['roomId', 'name', 'sortOrder'],
     shadeState: ['shadeId', 'position', 'target', 'direction', 'myPos', 'tiltPosition', 'tiltTarget', 'tiltDirection',
         'myTiltPos', 'flags', 'lastRollingCode'],