Merge the Documents/sras-viewer working copy into this repo

The two clones had diverged from origin/main (191d1b8) and both had
grown uncommitted work. This merges the other clone's three commits and
reconciles four conflicting files.

Both clones independently grew a feature called "batch export", but they
are different sweeps and both are kept:
- BatchExportWorker (this clone) — every angle x channel of the one open
  file, fixed colorbar per channel, under a new Export menu.
- BatchExportImagesWorker (other clone) — the current view across many
  selected files, process-pooled, under Convert.

Conflict resolutions of note:
- sras_average.py: the other clone's memory-bounded rewrite had silently
  reverted this clone's float32 -> int16 accumulator fix, which exists to
  keep averaged output from landing 1 ADC count off the original tool.
  Kept the rewrite, re-applied the fix, and corrected the two docstrings
  that still claimed float32.
- tests/test_compute.py: kept the other clone's meta["waveforms"] key
  (meta["data"] no longer exists for this fixture and would KeyError)
  and its laser_freq_hz assertions, plus this clone's int16 expectation
  and its dropped subprocess returncode assertions.
- ComputeWorker: row_avg_n and min_freq_mhz were added independently on
  either side; both are now threaded through.
- compute_rf_image's `exact` parameter is gone, removed by the other
  clone's PyFFTW peak-search rewrite. It had no remaining callers.

Verified: 149 passed with a complete dependency set. The failures seen
with this clone's own .venv are a missing scikit-image, which predates
this merge and reproduces identically on the pre-merge commit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

sras_viewer/dialogs.py

@@ -14,7 +14,6 @@ from PyQt6.QtWidgets import (
     QVBoxLayout, QWidget,
 )
 
-from sras_compute import PYFFTW_AVAILABLE
 from sras_format import CH1_IDX, CH3_IDX, CH4_IDX, CH_NAMES
 from sras_workers import ExportChannel
 
@@ -29,7 +28,7 @@ from .common import (
 # ---------------------------------------------------------------------------
 
 class FftOptionsDialog(QDialog):
-    """Configure FFT backend and zero-padding.
+    """Configure FFT zero-padding.
 
     Changes take effect only when the user clicks Apply.  Cancel discards
     all pending edits.  The live 'frequency resolution' label updates as
@@ -38,7 +37,6 @@ class FftOptionsDialog(QDialog):
     """
 
     def __init__(self, parent=None, *,
-                 current_backend: str,
                  current_pad_factor: int,
                  samples_per_frame: int | None,
                  sample_rate_hz: float | None,
@@ -54,29 +52,6 @@ class FftOptionsDialog(QDialog):
 
         layout = QVBoxLayout(self)
 
-        # ---- Backend ---------------------------------------------------
-        grp_backend = QGroupBox("FFT Backend")
-        bl = QVBoxLayout(grp_backend)
-
-        self._btn_scipy = QRadioButton("SciPy FFT (pocketfft)  (always available)")
-        self._btn_pyfftw = QRadioButton(
-            "pyFFTW  (faster for large arrays)" if PYFFTW_AVAILABLE
-            else "pyFFTW  (not installed — run: pip install pyfftw)")
-        self._btn_pyfftw.setEnabled(PYFFTW_AVAILABLE)
-
-        self._backend_group = QButtonGroup(self)
-        self._backend_group.addButton(self._btn_scipy, id=0)
-        self._backend_group.addButton(self._btn_pyfftw, id=1)
-
-        if current_backend == "pyfftw" and PYFFTW_AVAILABLE:
-            self._btn_pyfftw.setChecked(True)
-        else:
-            self._btn_scipy.setChecked(True)
-
-        bl.addWidget(self._btn_scipy)
-        bl.addWidget(self._btn_pyfftw)
-        layout.addWidget(grp_backend)
-
         # ---- Zero-padding ----------------------------------------------
         grp_zp = QGroupBox("Zero-Padding")
         zl = QVBoxLayout(grp_zp)
@@ -139,9 +114,6 @@ class FftOptionsDialog(QDialog):
             f"Velocity bin: {vel_res_ms:.3f} m/s  "
             f"(at grating = {self._grating_um:.2f} µm)")
 
-    def get_backend(self) -> str:
-        return "pyfftw" if self._btn_pyfftw.isChecked() and PYFFTW_AVAILABLE else "scipy"
-
     def get_pad_factor(self) -> int:
         return max(1, self._spin_pad.value())