acme looks like acme; every theme gets acme's button, scroll column and 2px rules

acme takes plan9port's own colours (acme.c iconinit, draw.h): selections
#eeee9e in the body and #9eeeee in the tag, black ink; exec and look sweeps
#aa0000 and #006600, white ink; a #99994c scrollbar under a #ffffea thumb;
black rules; a #8888cc tag/body rule and column button.

Every theme: the grip is acme's button, its tag row's full height, in one
scroll column with the scrollbar (rail_px, 12 at a 17px tagline, scaled,
times GripWidth, a percent, default 150; same x0/x1 to the pixel):
focused clean = solid box; focused dirty = box_dirty filled to a box ring
(acme's modbutton); unfocused clean = a box_border ring round the tag's
ground; unfocused dirty = box_dirty a pixel inside that ring. The grid, which
has no ring, marks dirty with a bold * on box_dirty in the grip's second cell
and fills an unfocused grip halfway to its ring. Regions carry a dirty flag.
Column buttons are the same shape, solid. 2px rules between columns and
stacked panes (inside the tag band's slack), none at the window edge; a 1px
tag/body rule halfway between tag and page.

Theme data: tag_sel_bg, sweep_bg/fg, tag_rule, rule_px, rail_px, box_border,
box_dirty. Chrome: rule_px, tag_rule, rail_px, grip_border, grip_focus_ring;
a comptime guard on Chrome's layout forces a wire bump once v8 ships.
Structural rules are exempt from the focus-indicator rule (docs/effects.md).

Tests: acme widths; stacked rule in the slack at two tagline sizes; every
grip-column pixel is band, button, ring or rule, and the button shares the
scrollbar's x0/x1 (4 metrics x top/bottom x focus x dirty); the four grip
states distinct in every native theme with a non-colour dirty cue in the
grid; wire round-trip of the new fields.

Shared files: src/colors.zig, src/surface.zig, src/body_layer.zig,
src/tagline.zig, src/detached/wire.zig, docs/themes.md, docs/config.md,
docs/effects.md, 21 snapshot goldens (the grip cells only),
test/gui-goldens.txt.

Motion flavours differ by design, and drive notice drops and pane moves

1 files changed, 4 insertions, 4 deletions

diff --git a/test/snapshots/theme.golden b/test/snapshots/theme.golden
index 4986eaae..5e7a3dc4 100644
--- a/test/snapshots/theme.golden
+++ b/test/snapshots/theme.golden
@@ -612,9 +612,9 @@
 |30: 0-0 d,#525252, 1-1 d,d, 2-49 #969696,#2c2a3e, 50-50 d,#525252, 51-51 d,d, 52-99 #969696,#2c2a3e,
 == snap acme grid=100x31 cursor=4,5
 == style acme grid=100x31
-|0: 0-50 #000000,#eaffff, 51-59 #000000,#fafa92, 60-70 #000000,#eaffff, 71-99 d,#eaffff,
-|1: 0-1 #000000,#c5a87f, 2-2 d,#eaffff, 3-34 #000000,#eaffff, 35-49 d,#eaffff, 50-51 #000000,#c5a87f, 52-52 d,#eaffff, 53-84 #000000,#eaffff, 85-99 d,#eaffff,
-|2: 0-1 #ffffff,#663fe0, 2-2 d,#eaffff, 3-49 #000000,#eaffff, 50-51 #ffffff,#353a58, 52-52 d,#eaffff, 53-99 #000000,#eaffff,
+|0: 0-50 #000000,#eaffff, 51-59 #000000,#9eeeee, 60-70 #000000,#eaffff, 71-99 d,#eaffff,
+|1: 0-1 #000000,#8888cc, 2-2 d,#eaffff, 3-34 #000000,#eaffff, 35-49 d,#eaffff, 50-51 #000000,#8888cc, 52-52 d,#eaffff, 53-84 #000000,#eaffff, 85-99 d,#eaffff,
+|2: 0-1 #000000,#8888cc, 2-2 d,#eaffff, 3-49 #000000,#eaffff, 50-51 #000000,#b9c3e5, 52-52 d,#eaffff, 53-99 #000000,#eaffff,
 |3: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |4: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |5: 0-99 d,#ffffea,
@@ -629,7 +629,7 @@
 |14: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |15: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |16: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
-|17: 0-1 #ffffff,#353a58, 2-2 d,#eaffff, 3-49 #000000,#eaffff, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
+|17: 0-1 #000000,#b9c3e5, 2-2 d,#eaffff, 3-49 #000000,#eaffff, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |18: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |19: 0-1 d,#ffffea, 2-49 #000000,#ffffea, 50-51 d,#ffffea, 52-99 #000000,#ffffea,
 |20: 0-51 d,#ffffea, 52-99 #000000,#ffffea,