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, 2 insertions, 2 deletions

diff --git a/test/snapshots/multicursor.golden b/test/snapshots/multicursor.golden
index 96762bd5..010199b1 100644
--- a/test/snapshots/multicursor.golden
+++ b/test/snapshots/multicursor.golden
@@ -52,13 +52,13 @@
 |29: 0-0 d,#608269, 1-1 d,#0d1410, 2-74 #e5eee5,#0d1410, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,
 |30: 0-0 d,#608269, 1-1 d,#0d1410, 2-74 #e5eee5,#0d1410, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,
 == snap edited-at-three grid=150x31 cursor=9,9
-|6:    /tmp/pardes-snap/multicursor/cwd/f.txt * Save Tty Collapse Del
+|6:  * /tmp/pardes-snap/multicursor/cwd/f.txt * Save Tty Collapse Del
 |7:      1 >>line 1
 |8:      2 >>line 2
 |9:      3 >>line 3
 == snap three-selections grid=150x31 cursor=8,9
 == style three-selections grid=150x31
-|6: 0-1 #000000,#add38a, 2-2 d,#26362d, 3-35 #becfc4,#26362d, 36-40 #dfbce5,#26362d, 41-64 #becfc4,#26362d, 65-74 d,#26362d, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,
+|6: 0-0 #000000,#add38a, 1-1 #000000,#f9cb70,b 2-2 d,#26362d, 3-35 #becfc4,#26362d, 36-40 #dfbce5,#26362d, 41-64 #becfc4,#26362d, 65-74 d,#26362d, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,
 |7: 0-0 d,#608269, 1-1 d,#0d1410, 2-6 #59675c,#0d1410, 7-7 #f5f7ee,#243a2d, 8-8 #3c614a,#f5f7ee, 9-14 #e5eee5,#0d1410, 15-74 d,#0d1410, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,
 |8: 0-0 d,#608269, 1-1 d,#0d1410, 2-6 #59675c,#0d1410, 7-7 #f5f7ee,#243a2d, 8-8 #3c614a,#f5f7ee, 9-14 #e5eee5,#0d1410, 15-74 d,#0d1410, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,
 |9: 0-0 d,#608269, 1-1 d,#0d1410, 2-6 #616f64,#0d1410,b 7-8 #f5f7ee,#3c614a, 9-14 #e5eee5,#0d1410, 15-74 d,#0d1410, 75-75 d,#608269, 76-76 d,#0d1410, 77-149 #e5eee5,#0d1410,