docs(omny): document manual tomo_alignment_fit offset nudge

Port the flomni doc addition to omny -- both setups share the identical
tomo_alignment_fit mechanism (OMNYAlignmentMixin.get_alignment_offset
mirrors Flomni's), so the same command-line offset nudge applies verbatim.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FFeiCHv3qUxxssmP9Qzhom

docs/user/ptychography/omny.md

@@ -378,6 +378,21 @@ The loading routine uses default values for the vertical alignment for setup. Th
 At each projection, the angular dependent is computed by  
 `omny.get_alignment_offset(angle)`, with _angle_ in degrees.
 
+To manually nudge the alignment by a few microns without recording a new fit,
+edit the constant offset term of the currently loaded fit directly:
+```python
+fit = omny.client.get_global_var("tomo_alignment_fit")
+fit[0][2] += 5.0   # x offset, microns
+fit[1][2] += 3.0   # y offset, microns
+omny.client.set_global_var("tomo_alignment_fit", fit)
+```
+`tomo_alignment_fit` is a 2x5 list (row 0 = x, row 1 = y); column 2 in each
+row is the constant offset of the sinusoidal fit
+(`correction = A*sin(angle + phase) + offset [+ 3rd-order term for y]`), so
+changing it shifts the correction by that amount at every angle without
+touching the fitted amplitude/phase. Check the result with
+`omny.get_alignment_offset(angle)`.
+
 The alignment can be cleared by  
 `omny.reset_tomo_alignment_fit()`