fix: AttributeError when selecting Simple Recording/Tracking tab

[hongquanli]

Summary

Selecting the Simple Recording tab (or Tracking tab) crashes with:

File "control/gui_hcs.py", line 2360, in onTabChanged
    acquisitionWidget.emit_selected_channels()
AttributeError: 'RecordingWidget' object has no attribute 'emit_selected_channels'

onTabChanged called emit_selected_channels() on whatever record tab was selected, but only the multipoint widgets (Flexible, Wellplate, Fluidics) define that method. Most machine configs have ENABLE_RECORDING off, which is why this went unnoticed. toggleAcquisitionStart had the same latent bug with display_progress_bar().

Fix (structural, no hasattr guards)

The first commit guarded both calls with hasattr; the second commit replaces that with a structural fix:

Channels: emit at acquisition start, not tab change. The napari multichannel viewer needs two inputs: shape and channels. Shape was already emitted at acquisition start (next to signal_acquisition_started); channels rode on tab change. Now emit_selected_channels() is called at the same acquisition-start point in all three multipoint widgets — Wellplate's _set_ui_acquisition_running covers both the button path and the TCP/invokeMethod path. onTabChanged no longer calls anything on the selected tab, so tabs without channel selections are never asked. Timing is safe: the only consumer of the channel set (updateLayers) runs exclusively during an acquisition, and the per-tab itemSelectionChanged connections still keep it fresh in between.

Progress bar: delete the gui_hcs call. Every widget with a progress bar already connects its own signal_acquisition_started to its own display_progress_bar, and toggleAcquisitionStart is only ever invoked via that same signal — the call in gui_hcs was redundant for multipoint tabs and a crash for the rest.

Testing

• Regression test: builds the simulated GUI with ENABLE_RECORDING patched on, switches to the Simple Recording tab, and cycles toggleAcquisitionStart — reproduced the exact AttributeError before the fix, passes after.
• New test: signal_acquisition_channels is emitted at acquisition start with the selected channel names.
• All 4 tests in tests/control/test_HighContentScreeningGui.py pass locally with QT_API=pyqt5 (this file is skipped in CI).
• black clean.

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