Fix/linewidth - #170

Changed to linewidth:

theme_cmap.R — geom_hline/geom_vline (the origin lines), all six element_line() calls (gridlines, axis lines, ticks), the base line element, and the element_rect() border in theme_cmap_base().
default_aes.R — the GeomLine default only.
geom_recessions.R / geom_pandemics.R — the GeomRecessions/GeomPandemics default_aes (size = 0.5 → linewidth = 0.5) and their draw code (lwd = coords$size → coords$linewidth), kept internally consistent.

Left as size (correctly): all element_text() font sizes, the text-geom defaults (3.88, fsize/.pt), and the point-geom sizes (GeomPointLast, and the coords$size in the point-drawing code).
DESCRIPTION: bumped ggplot2 to >= 3.4.0 in Depends — linewidth was introduced there, so this is now the real floor.
Each replacement ran with an exact occurrence-count assertion, so nothing over-matched, and all four R files are brace-balanced and untruncated.
Fix typo: theme_cmap_base() read $fgiont instead of $font

The `text` element in theme_cmap_base() referenced
cmapplot_globals$fgiont$regular$face, which resolved to NULL and
dropped the base theme's default font face. Corrected to $font.