fix: enable radio.rxgain CLI command for LR1110 (T1000-E)

[jirogit]

Problem

radio.rxgain get/set commands were broken on T1000-E (LR1110).

The CLI branches in CommonCLI.cpp were guarded by
#if defined(USE_SX1262) || defined(USE_SX1268), but USE_LR1110 was
not defined in the T1000-E build, so both branches were compiled out.

This caused two different failure modes:

• get radio.rxgain → returned the full radio config string (e.g.
  > 921.000,125.0,10,5) because memcmp("radio", 5) matched the
  next branch
• set radio.rxgain on → returned unknown config: radio.rxgain on
  because no branch matched

Fix

• Add -D USE_LR1110 to variants/t1000-e/platformio.ini
• Add USE_LR1110 to the #if guard on both get and set branches

CustomLR1110Wrapper already implements setRxBoostedGainMode() and
getRxBoostedGainMode() via the RadioLibWrapper virtual interface —
no radio-layer changes required.

Testing (T1000-E)

• get radio.rxgain → > off ✅
• set radio.rxgain on → OK ✅
• get radio.rxgain after reboot → > on ✅

[jirogit]

This also partially addresses #2118.
The root cause of that issue (rxgain defaulting to OFF on upgrade)
is separate, but on T1000-E (LR1110) the CLI command was completely
non-functional, so users had no way to restore the setting even manually.
This fix enables set radio.rxgain on to work on T1000-E.