feat: rotate and wrap long axis tick labels

[schochastics]

Closes the last WI-4 residual: wrapping/auto-fit for long axis tick labels (title/subtitle/caption already wrap). Two mechanisms, both driven from the theme.

Rotation

axis.text.x / axis.text.y now honour an angle — previously a silent no-op. .draw_axis reads the element's rotation, passes rot= to the label grob, and anchors it: an explicit hjust/vjust wins, otherwise the end of the run is pinned at the tick so the slant clears the panel. The gutter/row is sized from the rotated extent (the existing .track_w/.track_h rot path).

vplot(gdp) |> mark_bar(x = country, y = score) |>
  theme(axis.text.x = element_text(angle = 45))

Wrapping

Left horizontal, a long discrete label that would overrun its tick spacing wraps onto multiple lines and the label row grows to fit. At layout time — when the page width is known and the panel is a plain null track — each tick's mm budget (panel width ÷ break count) is computed via vellum::vl_convert() and handed to the drawer as an absolute wrap width; the row is measured through the same grob (.axis_text_grob) so the reserved height matches the drawn text.

Byte-identical guarantee: wrapping only engages when the widest label actually overruns its budget, so every plot whose labels already fit is unchanged (all existing snapshots pass untouched). Rotated, aspect-locked (coord_fixed/coord_sf/polar), faceted-free-x, marginal, and aligned-composition paths fall back to single line.

Also: .el_rot() is now blank-safe (element_blank() carries no angle property).

Verification (WI-0)

Rendered and looked at 45°, 90°, and wrapped bar charts (labels rotate/wrap, clear the panel, row height reserved, no overlap); confirmed a rotated axis renders through vellumwidget::as_widget(); inst/examples/32-axis-labels.R runs end to end.

Tests: test-axis-text.R (13). Full suite [ FAIL 0 | WARN 1 pre-existing | SKIP 0 | PASS 2873 ].

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