v1.87.0

Added

• PNG/bokeh regression diagnostic plot via render_regression_png (matplotlib) and build_regression_overlay (holoviews/bokeh) sharing a single plot spec, so the same diagnostic can be posted as a PR-comment PNG or embedded in the HTML report. RegressionResult now stores history/current samples and their over_time coordinates so plots use real datetimes when available.
• HTML report auto-inserts the regression overlay per regressed variable; bare over_time line/band plots are suppressed for any variable with a regression overlay to avoid duplicate graphs.
• Categorical x-axis support in regression plots (e.g. git_time_event string labels like "2024-06-15 abc1234d"), surfaced via xticks overrides.
• Dotted connector from the last history point to the current marker in regression overlays so the jump that triggered a regression is visually obvious.
• matplotlib added as a dependency for PNG rendering.

Fixed

• over_time bar plot crash on duplicate coord values (e.g. two runs at the same git_time_event string) that caused HoloMap must only contain one type of object, not both Bars and DynamicMap. Switched _build_time_holomap and _pane_over_time_{slider,grid} to positional isel(over_time=idx) and deduped identical coord values.
• Holoviews UFuncNoLoopError with git_time_event string x-axes by replacing HSpan/HLine with Area/Curve primitives that carry explicit x coords, so the regression band and baseline always render regardless of x dtype.
• Regression plot dtype mismatch between hist_x and current_x (e.g. datetime64 vs int64) that raised in holoviews' range computation; current_x now only replaces the extrapolated tick when its dtype matches the history.
• Single-datetime-point regression overlays now nudge the current marker forward by a small timedelta so it doesn't overlap the sole history point.