Closes #2229

Problem

SWR sweep aborts with SWR sweep stopped: no fresh TGXL SWR meter data whenever the user has a TGXL in OPERATE mode at sweep start.

The pre-sweep logic at MainWindow.cpp:10854-10856 selects meterSource = Tgxl, then commands the TGXL into BYPASS to measure raw antenna SWR. Once in bypass the TGXL is a passive wire-through — its measurement engine stops emitting RL (return-loss → SWR) meter packets, so tgxlSwrUpdatedAtMs() never advances past sampleNotBeforeMs and the per-step freshness check times out at 900 ms.

Fix

While the TGXL is bypassed, the radio's own SWR coupler sees the same physical signal — the radio measures directly through the bypassed TGXL relays. The reading is equivalent and arrives reliably during the tune carrier.

Switch the meter source to Radio while keeping the "TGXL BYPASS" UI label so users still see what configuration is in use.

if (tuner.isPresent() && tuner.isOperate()) {
    m_swrSweep.sourceLabel = QStringLiteral("TGXL BYPASS");
    // Read radio-side SWR even when TGXL is bypassed: in bypass the TGXL
    // is a passive wire-through and stops emitting RL meter packets, so
    // tgxlSwrUpdatedAtMs never advances.  The radio's SWR coupler sees
    // the antenna directly through the bypassed relays — equivalent
    // reading, reliably emitted during the tune carrier.  (#2229)
    m_swrSweep.meterSource = SwrSweepMeterSource::Radio;
    if (!tuner.isBypass()) {
        m_swrSweep.tgxlBypassRequested = true;
        m_swrSweep.tgxlRestoreNeeded = true;
    }
}

Test plan

• Build clean on Linux
• On-air test with FLEX-8600 + TGXL in OPERATE — sweep runs to completion, TGXL restored to OPERATE after sweep
• CI green

Follow-up

The SwrSweepMeterSource::Tgxl branch is now effectively dead — no operating mode prefers TGXL meters over radio meters during a sweep (TGXL OPERATE during sweep would defeat the raw-antenna-SWR purpose; BYPASS makes the radio reading equivalent and more reliable). Could be removed in a follow-up cleanup PR.

cc @jensenpat — small fix on top of your AetherSweep work.

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