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, 1 deletions

diff --git a/docs/effects.md b/docs/effects.md
index fec2d13b..eefa52d3 100644
--- a/docs/effects.md
+++ b/docs/effects.md
@@ -6,7 +6,10 @@ selection) or reduce its contrast. The effects are sugar; the indicators are
 how a person knows where they are. Every G stage is reviewed against this.
 Lift, for one, falls only on pane bodies and rails, never on a tag, a grip or
 a header, and its strength is capped so text and the selection keep min(their
-contrast, 4.5) (tests in src/gui/gui.zig). A dim touches only the unfocused
+contrast, 4.5) (tests in src/gui/gui.zig). The rule binds effects, not a
+theme's structure: the rules between panes (2px, `rule_px`) are the theme's
+borders, and the one over a tag band stays in the band's slack, never over
+its text. A dim touches only the unfocused
 panes, with the same floor, and the focused pane's text is never at less
 contrast than theirs (tests in src/draw.zig).