Align axes across stacked plots

[phfix]

Summary

Stacked plots can become visually misaligned when different plots need different amounts of space for axis labels.

Examples:

• vertically stacked plots with different Y-axis label widths
• horizontally stacked plots with different X-axis label heights or date/time labels

This causes the plot canvases to start at different positions, making cross-plot comparison harder.

Expected behavior

When plots are stacked in the same plot container, their canvases should align even if their axis labels have different extents.

This should work for:

• vertical stacking: align the left Y-axis extent so X-axis start positions match
• horizontal stacking: align the bottom X-axis extent so plot areas line up vertically

Proposed behavior

Use one user-facing option to enable/disable axis alignment across stacked plots.

Suggested behavior:

• enabled by default
• applies within the same stacked plot container/tab
• uses the maximum required axis extent among sibling plots
• applies to both left Y-axis and bottom X-axis layout extents

Motivation

Without alignment, stacked plots with different axis label sizes look uneven and make it harder to compare events at the same time position across plots.

Possible implementation approach

• measure the natural extent of each plot's left and bottom axes
• compute the maximum extent across the container
• apply that as the minimum extent for sibling plots before replotting
• expose a single preference flag such as align_axes

Affected areas

• plotjuggler_app/plot_docker.cpp
• plotjuggler_base/include/PlotJuggler/plotwidget_base.h
• plotjuggler_base/src/plotwidget_base.cpp
• plotjuggler_app/preferences_dialog.cpp
• plotjuggler_app/preferences_dialog.ui

[phfix]

Implemented in commit 3865a91 (Align axes across stacked plots) and pushed to main. This still needs runtime testing for both vertical and horizontal stacking behavior, and for the new Align axes across stacked plots preference toggle.

[phfix]

Update after testing: the main stacked-axis misalignment is improved by aligning Qwt minimum extents in addition to axis widget size. There still appears to be a residual ~1 pixel vertical/layout difference in some cases (for example canvas y / bottom-axis geometry differing by 1 px between adjacent plots). The larger left-edge X-axis alignment problem seems addressed; the remaining 1 px mismatch should be treated as follow-up polish rather than the main bug.